Non-Suicidal Self-Injury in Adolescents:

Executive Functions and the Role of Serotonin in Impulsivity

Linn T. Fikke

The Cognitive Developmental Research Unit

Department of Psychology

Faculty of Social Sciences

University of Oslo

2011

© Linn T. Fikke, 2011 Series of dissertations submitted to the Faculty of Social Sciences, University of Oslo No. 282 ISSN 1504-3991 All rights reserved. No part of this publication may be reproduced or transmitted, in any form or by any means, without permission. Cover: Inger Sandved Anfinsen. Printed in Norway: AIT Oslo AS. Produced in co-operation with Unipub, Oslo. The thesis is produced by Unipub merely in connection with the thesis defence. Kindly direct all inquiries regarding the thesis to the copyright holder or the unit which grants the doctorate.

Contents

Acknowledgements

1

List of Papers

3

List of Abbreviations

4

The Theme of this Thesis

5

Introduction

7

Self-Injurious Behaviours 7 Non-Suicidal Self-Injury 9 Executive Functions in Emotion Regulation 18 The Neuropsychology of Self-Injurious Behaviours in General and NSSI in Particular 20 Serotonin in Self-Injurious Behaviours, NSSI, Emotion Regulation and Impulsivity 23 Main Research Aims

25

Paper I 25 Paper II 25 Paper III 25 Materials and Methods

26

Design 26 Participants and Procedures 26

The screening session 27 The test session 28 The experimental session 29

Behavioural and Clinical Measures 31 Clinical measure in the screening session 31 Clinical measures in the test session 32 Neuropchychological measures in the test session 33

Behavioural measures in the experimental session 38 Assessment of Plasma Tryptophan Concentration in the Experimental Session 40 Statistical Analyses 40

Paper I 41 Paper II 41 Paper III 42

Ethical Considerations 42

Results

45

Paper I 45 Paper II 46 Paper III 48 Summary of Papers

50

Paper I 50 Paper II 50 Paper III 51 Discussion

53

Discussion of Main Findings 53 Findings with respect to impulsivity across NSSI subgroups and sessions 57 The use of different NSSI subgroups 61 The influence of sex on the neuropsychological findings in adolescents engaging in NSSI

64

Methodological Considerations 65 Reliability of findings 65 External validity of findings 66

Clinical Implications 69 Future Perspectives 71 Conclusions

76

References

77

Papers I-III

100

1

Acknowledgements

First, I would especially like to thank my supervisor Professor Nils Inge Landrø for all

his good advice. He shared his invaluable knowledge and insight from the very beginning in

generating ideas, the implementation of them, the discussion of findings and the completion in

writing. I would also like to thank the head of the Cognitive Developmental Research Unit,

Associate Professor Annika Melinder, for providing the fundings and all the necessary

material aids for the study. As my co-supervisor, I am also grateful for her invaluable help in

the clinical parts of the study.

I am very grateful to all the adolescents participating in the study. I could always rely

on them to meet at the scheduled times! Also, I thank the schools and the teachers for their

help in recruiting adolescents to participate in the study.

I would especially like to thank Ragnhild Bø and Øyvind Bastnes Lie for their

invaluable assistance in collecting and processing data as well as for helpful discussions. I am

also thankful to Espen Walderhaug for introducing me to the acute tryptophan depletion

procedure, and for always being so helpful. I am also grateful to my very good colleague Else

Marie Augusti for all her support and important contributions. Thank you to all my colleagues

at the Department of Psychology in general and the Cognitive Developmental Research Unit

in particular at the University of Oslo for their help.

I also thank our colloborators at the Institute of Forensic Medicine at the University of

Oslo, Ann Cathrin Larsen, Sara Moberg, Hang Duong Thi Tuyet and Torleif Rognum for

generously providing expertise in their field.

The work has been supported by grants from the Ministry of Children, Equality and

Social Inclusion and the Norwegian Directorate for Children, Youth and Family Affairs, for

2

which I am grateful. Thank you to the Department of Psychology at the University of Oslo for

the opportunity to participate in the PhD programme.

Thank you to my parents for always providing the best conditions for me to work in,

and for their invariable help, especially in the writing process. Last, but not least, thank you so

much Andreas for the thousand things you have done for me!

3

List of Papers

1. Fikke, L. T., Melinder, A., & Landrø, N. I. (2011). Executive functions are impaired in

adolescents engaging in non-suicidal self-injury. Psychological Medicine, 41, 601-

610. doi:10.1017/S0033291710001030

2. Fikke, L. T., Landrø, N. I., & Melinder, A. (2010). Working Memory and Verbal

Learning are Impaired in Adolescents Engaging in Non-Suicidal Self-Injury. (Under

review).

3. Fikke, L. T., Melinder, A., & Landrø, N. I. (2011). Acute tryptophan depletion

influences impulsivity but not mood in adolescents engaging in non-suicidal self-

injury. (Under review).

4

List of Abbreviations

5-HT 5-Hydroxytryptamine, Serotonin ADHD Attention Deficit Hyperactivity Disorder ANOVA Analysis of Variance ATD Acute Tryptophan Depletion BAI Beck Anxiety Inventory BDI Beck Depression Inventory BPD Borderline Personality Disorder CANTAB Cambridge Neuropsychological Test Automated Battery CAVLT-2 Children’s Auditory Verbal Learning Test-2 CPT Continuous Performance Test CPT-IP Continuous Performance Test, Identical Pairs Version DSM-IV Diagnostic and Statistical Manual of Mental Disorders, 4th edition DSM-V Diagnostic and Statistical Manual of Mental Disorders, 5th edition EF Executive Functions FASM Functional Assessment of Self-Mutilation FSIQ Full-Scale Intelligence Quotient IED Intra/Extradimensional IGT Iowa Gambling Task IQ Intelligence Quotient K-SADS-PL Kiddie-Sads-Present and Lifetime Version MDD Major Depressive Disorder MFF20 Matching Familiar Figures Test NAD Nicotine-adenine dinucleotide NSD Norwegian Social Science Data Services NSSI Non-Suicidal Self-Injury PIQ Performance Intelligence Quotient POMS Profile of Mood States PTSD Post-Traumatic Stress Disorder SSRI Selective Serotonin Reuptake Inhibitor SSRT Stop Signal Reaction Time SST Stop Signal Task STAXI State-Trait Anger Expression Inventory SWM Spatial Working Memory TMD Total Mood Disturbance VIQ Verbal Intelligence Quotient WASI Wechsler Abbreviated Scale of Intelligence

5

The Theme of this Thesis

In the last few decades, there has been an increased focus on non-suicidal self-injury in

general and in adolescents in particular. Research findings show that non-suicidal self-injury

is alarmingly widespread even in community samples of adolescents. Furthermore, non-

suicidal self-injury is associated with psychological suffering, such as depression, suicidality,

and anger problems, emphasizing the seriousness of this behaviour. However, little is known

of underlying factors that can be involved in non-suicidal self-injury. In particular, research

investigating the possible roles of neuropsychological and serotonin functions in non-suicidal

self-injury in adolescents is scarce. One main aim of this dissertation was therefore to

investigate various aspects of neuropsychological functions in adolescents engaging in non-

suicidal self-injury. Another main aim was to investigate the effects of low serotonin function

on impulsivity and mood in female adolescents engaging in non-suicidal self-injury. To

examine these research aims, community sampled adolescents were recruited to participate in

the study involving three sessions; a screening session, a test session and an experimental

session. In the test session, a comparative cross sectional design was used to investigate

neuropsychological functions in adolescents engaging in non-suicidal self-injury as compared

with a healthy control group. In the experimental session a randomized double-blind placebo-

controlled parallel group design was used. Specifically, the effects on impulsivity and mood

of an experimentally induced lowering of serotonin, via acute tryptophan depletion, were

investigated in female adolescents engaging in non-suicidal self-injury. The findings from this

study could help illuminate various aspects of neuropsychological and serotonergic

functioning that might be involved in non-suicidal self-injury in adolescents. In a theoretical

perspective, the findings could yield knowledge about neuropsychological factors involved in

non-suicidal self-injury, thereby contributing to the puzzle of understanding why adolescents

6

engage in non-suicidal self-injury, at least from a neuropsychological perspective. Also, the

findings from the study could yield valuable knowledge about neuropsychological as well as

serotonin functioning that should be targeted in applied and clinical settings to help

adolescents discontinue engaging in non-suicidal self-injury as well as to reduce possible

functional consequences of deficits in specific neuropsychological functions.

7

Introduction

Self-Injurious Behaviours

The phenomena of self-injury has existed for thousands of years. Acts of self-injury

are described in the Old Testament in 3 Kings 18:28; “ So they cried with a loud voice and cut

themselves after their manner with knives and lancets till they were all covered with blood,”

as well as in the New Testament in Mark 5:5; “…and he was always day and night in the

monuments and in the mountains crying and cutting himself with stones.”

The field of self-injurious behaviours has been troubled by inconsistent terminology

(Jacobsen & Gould, 2007; Muehlenkamp, 2005; Skegg, 2005). Numerous terms are used to

refer to the various phenomena within the field (Muehlenkamp, 2005). Examples of these

terms are: self-mutilation (Briere & Gil, 1998; Favazza, 1998), deliberate self-harm (Gratz,

Conrad, & Roemer, 2002; Hawton, Rodham, Evans, & Weatherall, 2002), parasuicidal

behaviour (Linehan, Armstrong, Suarez, Allmon, & Heard, 1991), self-injurious behaviour

(Ohmann et al., 2008), non-suicidal self-injury (NSSI; Lloyd-Richardson, Perrine, Dierker, &

Kelley, 2007), self-cutting (Hintikka et al., 2009) and self-inflicted injury (Jablonska et al.,

2009). Importantly, different terms are used to refer to the same phenomena, whereas the

same term is used to refer to different phenomena in various research groups (Jacobsen &

Gould, 2007). For instance, in North America, “deliberate self-harm” refers to the deliberate,

direct destruction or alteration of body tissue without suicidal intent (Gratz et al., 2002),

whereas in the United Kingdom, “deliberate self-harm” refers to any deliberate self-injurious

or self-poisoning act with a non-fatal outcome, regardless of suicidal intent (Hawton et al.,

2002). Thus, several researchers (Hawton et al., 2002, 2003; Hurry, 2000) do not separate

either 1) indirect from direct self-harm or 2) suicidal behaviours, i.e., behaviours engaged in

8

with the intent to die as a result of the acts, from self-injurious behaviours without suicidal

intent.

NSSI refers to the deliberate, direct destruction or alteration of body tissue without

conscious suicidal intent (Favazza, 1998; Lloyd-Richardson et al., 2007). NSSI is

differentiated from indirect self-harm, such as overdose, drinking and driving and self-

poisoning, and is socially unacceptable, as opposed to for instance ear piercing and

professionally applied tattooing (Lloyd-Richardson et al., 2007; Walsh & Rosen, 1988).

Examples of NSSI are cutting, carving, and burning skin, hitting self and picking at wounds

(Favazza, 1998; Lloyd-Richardson et al., 2007).

Indeed, multiple lines of arguments and research findings suggest that NSSI is distinct

and so should be differentiated from suicidal behaviours (Muehlenkamp, 2005). First, the

obvious difference between NSSI and suicidal behaviours is the intent of the behaviours;

NSSI is engaged in with no intent to kill oneself and thus is engaged in for reasons other than

to end one’s life, while suicidal behaviours are engaged in to kill oneself (O’Carroll et al.,

1996; Simpson, 1980). Specifically, NSSI is often engaged in to alter one’s general state of

mind or consciousness, not to terminate consciousness as is the goal of engaging in suicidal

behaviours (Walsh & Rosen, 1988). Second, individuals generally report feeling better after

having engaged in NSSI, their state of mind is altered and their tension reduced, whereas in

individuals committing suicide, whatever relief is to be gained is experienced before their

suicidal act (Walsh & Rosen, 1988). Along these lines, individuals engaging in NSSI are most

interested in what happens after having engaged in NSSI, whereas individuals committing

suicide will never experience the results of their suicidal act alive (Walsh & Rosen, 1988).

Relatedly, adolescents engaging in NSSI reported more positive attitudes towards life as

compared with adolescents with previous suicide attempts (Muehlenkamp & Gutierrez, 2004).

9

Third, at the individual level NSSI typically is engaged in repetitively, involves the use of

several methods and consists of low-lethality behaviours (Simpson, 1980; Walsh & Rosen,

1988). This contrasts with suicidal behaviours which at the individual level typically occur

infrequently, do not involve the use of multiple methods and involve high lethality (Walsh &

Rosen, 1988). Fourth, NSSI differs from suicidal behaviours with respect to demographic

characteristics (see Muehlenkamp, 2005, for a review). NSSI is more prevalent than suicide

attempts and completed suicide combined. Also, NSSI is more prevalent in adolescence,

while completed suicide is more common in adults (Muehlenkamp, 2005). Furthermore,

several findings show similar prevalence rates of NSSI in boys and girls (Garrison et al.,

1993; Muehlenkamp & Gutierrez, 2004; Zoroglu et al., 2003, but see Laye-Gindhu &

Schonert-Reichl, 2005; Muehlenkamp & Gutierrez, 2007; Ross & Heath, 2002), while

completed suicides are more common in males, at least in the Western part of the World (see

Gould, Greenberg, Velting, & Shaffer, 2003, for a review). In sum, these arguments and

findings supporting considerable differences between NSSI and suicidal behaviours should

not be overlooked. They implicate that different prevention and treatment efforts are needed

with respect to NSSI and suicidal behaviours, respectively (Muehlenkamp, 2005).

Non-Suicidal Self-Injury

In one classification scheme, NSSI is divided into three main categories based on

degree of tissue destruction and the rate and pattern of behaviour (Favazza, 1998). Major self-

injury involves dramatic and extreme albeit infrequent acts such as autocastration, self-

enucleation and limb amputation (Favazza, 1998; Stanley, Winchel, Molcho, Simeon, &

Stanley, 1992) and is most often associated with psychosis and acute intoxiations (Favazza,

1998; Jacobsen & Gould, 2007). Individuals often explain their acts of major self-injury with

reference to religious and/or sexual themes such as spiritual purification, punishment for sins,

10

response to heavenly commands and visions and rescission of troublesome genitals (Favazza,

1998).

Stereotypic self-injury are often repetitive and sometimes rhytmic and refers to acts

such as head banging, hitting and self-biting (Favazza, 1998; Stanley et al., 1992). Stereotypic

self-injury is engaged in by individuals with Lesch-Nyhan syndrome, mental retardation,

and/or pervasive developmental disorders such as autism (Favazza, 1998; Jacobsen & Gould,

2007; Nyhan, 2005; Stanley et al., 1992).

Superficial/moderate self-injury can be subdivided into the compulsive and the

episodic types, respectively (Favazza, 1998). Compulsive superficial/moderate self-injury

involves acts such as skin picking and trichotillomania (Favazza, 1998). Indeed, findings

implicate partly overlapping neurobiological underpinnings to trichotillomania (compulsive

hair pulling) and obsessive-compulsive disorder (Chamberlain, Fineberg, Blackwell, Robbins,

& Sahakian, 2006). Episodic superficial/moderate self-injury refers to acts such as skin

cutting, carving and burning (Favazza, 1998). When self-injuring acts of the episodic type

become an overwhelming preoccupation, episodic becomes repetitive self-injury (Favazza,

1998). However, there are no clear cut objective, observable criteria defining “overwhelming

preoccupation.” The switch from episodic to repetitive self-injury is indeed described as

“fluid” (Favazza, 1998). For purposes of the present research project, we focused exclusively

on NSSI occurring as episodic/repetitive superficial/moderate self-injury. Thus, in the

following we refer exclusively to this category of NSSI when using the term “NSSI”.

Until at least quite recently, engaging in NSSI has been associated mainly with

individuals with personality disorders, especially borderline personality disorder (BPD;

Stanley et al., 1992; Zanarini, Gunderson, Frankenburg, & Chauncey, 1990). Indeed, recurrent

suicidal behaviour, gestures, or threats, or self-mutilating behaviour is one of the criteria for a

11

diagnosis of BPD in the Diagnostic and Statistical Manual of Mental Disorders, 4th edition

(DSM-IV; American Psychiatric Association, 1994). However, recent research findings show

that community sampled as well as outpatient and inpatient adolescents and young adults with

a history of NSSI are a heterogeneous group with respect to psychiatric symptoms and

diagnoses (Hintikka et al., 2009; Jacobsen, Muehlenkamp, Miller, & Turner, 2008; Nock,

Joiner, Gordon, Lloyd-Richardson, & Prinstein, 2006; Nock & Mendes, 2008). In addition, a

considerable number of them does not meet criteria for any axis I DSM-IV diagnoses, such as

with 12% of inpatient adolescents (Nock et al., 2006) and 21% of community sampled

adolescents (Hintikka et al., 2009). Accordingly, it has been suggested that NSSI should be an

independent, distinct axis I diagnosis as an impulse control disorder (Favazza, 1998), as a

deliberate self-injury syndrome (Muehlenkamp, 2005) or as a deliberate self-harm syndrome,

characterized by multiple recurrent episodes of low lethality self-harm deliberately inflicted

upon the body (Pattison & Kahan, 1983). Indeed, NSSI is proposed as a separate diagnostic

category in the Diagnostic and Statistical Manual of Mental Disorders, 5th edition (DSM-V;

American Psychiatric Association, 2010).

NSSI is alarmingly widespread in adolescents. As many as 61% of adolescent

psychiatric inpatients reported ever having engaged in NSSI (DiClemente, Ponton, & Hartley,

1991). Indeed, in a recent study, 82% of adolescent psychiatric inpatients had engaged in

NSSI during the previous 12 months (Nock & Prinstein, 2004). Even in community samples

of adolescents, lifetime prevalence rates of NSSI range from 14% - 23% (Muehlenkamp &

Gutierrez, 2004, 2007; Ross & Heath, 2002; Zoroglu et al., 2003). Furthermore, in young

community adolescent girls, 56% reported having engaged in NSSI during their lifetime (Hilt,

Cha, & Nolen-Hoeksema, 2008). During a 12-month period, as many as 46% of community

sampled adolescents reported having engaged in NSSI (Lloyd-Richardson et al., 2007). It has

12

been speculated whether prevalence rates of NSSI among community sampled adolescents are

increasing (Jacobsen & Gould, 2007). However, findings based on data from 2001 to 2005

suggest that although overall lifetime rates of NSSI among community sampled adolescents

may fluctuate across years, they generally have remained consistent (Muehlenkamp,

Williams, Gutierrez, & Claes, 2009). Equal prevalence rates in NSSI between females and

males were found during the first 3 years. However, during the last 2 years of the study, the

rate of NSSI among females increased significantly, whereas males’ rates of NSSI declined

(Muehlenkamp et al., 2009). Relatedly, there are mixed findings with respect to sex-

differences in prevalence rates of NSSI. In adolescent psychiatric patients, Nock and Prinstein

(2004) found no sex-difference in prevalence rates of NSSI, whereas Jacobsen et al. (2008)

found that females are more likely to engage in NSSI as compared with males. Likewise, in

community sampled adolescents, some find a higher prevalence rate in females than in males

(Laye-Gindhu & Schonert-Reichl, 2005; Muehlenkamp & Gutierrez, 2007; Ross & Heath,

2002), whereas others find no such sex-difference (Garrison et al., 1993; Muehlenkamp &

Gutierrez, 2004; Zoroglu et al., 2003). Onset of NSSI behaviours is typically reported to be

between 12 and 14 years of age in both community sampled adolescents (Muehlenkamp &

Gutierrez, 2007; Ross & Heath, 2002) and in adolescent psychiatric inpatients (Nock &

Prinstein, 2004).

NSSI is a heterogeneous phenomenon, ranging from minor to severe forms (Lloyd-

Richardson et al., 2007). Cutting, scratching and self-hitting were among the top four methods

used to self-injure in community sampled adolescents (Laye-Gindhu & Schonert-Reichl,

2005; Muehlenkamp & Gutierrez, 2004, 2007; Ross & Health, 2002). Similarly, cutting,

picking at a wound, scraping and self-hitting were among the most common methods used to

self-injure in clinical adolescent samples (Guertin, Lloyd-Richardson, Spirito, Donaldson, &

13

Boergers, 2001; Nock & Prinstein, 2004). Whether all behaviours that qualify for NSSI

according to the definition are of clinical significance are unresolved issues (Lloyd-

Richardson et al., 2007). For instance, picking at a wound may in isolation reflect non-

pathological, non NSSI (Lloyd-Richardson et al., 2007), suggesting that engaging in

behaviours that meet the criteria for NSSI might not in iself be of clinical significance.

Nevertheless, it appears that those who are engaging in several NSSI behaviours also are

picking at wounds, in a self-injuring way, as opposed to benign picking at a scab etc. (E. E.

Lloyd-Richardson, personal communication, October 10, 2007). Exploring why the particular

adolescent engages in NSSI behaviours and thoroughly assessing associated psychological

suffering might be some of the relevant factors when examining whether NSSI behaviours are

of clinical significance for the individual adolescent.

It has been suggested to classify NSSI behaviours into three groups based on their

potential for causing tissue damage (Skegg, 2005; Whitlock, Muehlenkamp, & Eckenrode,

2008). The first group includes behaviours with the potential for superficial tissue damage,

such as scratching until marks remain on the skin or bleeding occurs. Behaviours that often

cause bruising or light tissue damage, such as punching oneself or other objects, are

encompassed in the second group. The third group includes behaviours that likely cause

severe tissue damage, such as cutting, carving or burning areas of the body (Whitlock et al.,

2008). The three groups of NSSI behaviours reflect increasingly severe forms of NSSI

(Whitlock et al., 2008). Supporting this classification, NSSI forms as categorized into one of

the three groups, was one important characteristic in classifying individuals engaging in

NSSI, into different subgroups (Whitlock et al., 2008). Although the picture is not completely

consistent (Nock & Prinstein, 2004), some find sex differences in the forms of NSSI engaged

in in adolescents and young adults (Whitlock et al., 2008). For instance, in community

14

sampled adolescents, males were more likely to engage in self-battery, whereas females were

more likely to report cutting and severe scratching (Muehlenkamp, Yates, & Alberts, 2004 as

cited in Whitlock et al., 2008).

NSSI is associated with a range of psychiatric symptoms and diagnoses. In inpatient

adolescents having engaged in NSSI in the previous 12 months, 88% met criteria for at least

one DSM-IV axis I diagnosis (Nock et al., 2006). Specifically, 42% met criteria for major

depressive disorder (MDD), 24% met criteria for post-traumatic stress disorder (PTSD), 16%

met criteria for generalized anxiety disorder, 50% met criteria fror conduct disorder, 45% met

criteria for oppositional defiant disorder and 60% met criteria for any substance use disorder.

Likewise, Jacobsen et al. (2008) found elevated rates of MDD (46%), dysthymia (28%),

PTSD (6%), any anxiety disorder (32%), any eating disorder (8%), any disruptive behaviour

disorder (33%) and any substance use disorder (7%) among outpatient adolescents with a

recent history of NSSI. Even in adolescent community samples, NSSI is associated with

expressions of psychological distress, such as elevated levels of depressive (Laye-Gindhu &

Schonert-Reichl, 2005; Ross & Heath, 2002) and anxious symptoms (Ross & Heath, 2002)

and anger control problems (Laye-Gindhu & Schonert-Reichl, 2005). Also in community

sampled adolescents, NSSI is associated with MDD (Garrison et al., 1993; Hintikka et al.,

2009), anxiety disorders (Garrison et al., 1993; Hintikka et al., 2009) and eating disorders

(Hintikka et al., 2009). Furthermore, NSSI is associated with suicide ideation (Garrison et al.,

1993; Laye-Gindhu & Schonert-Reichl, 2005; Lloyd-Richardson et al., 2007), suicide plans

(Laye-Gindhu & Schonert-Reichl, 2005) and suicide attempts (Laye-Gindhu & Schonert-

Reichl, 2005; Lloyd- Richardson et al., 2007) in community samples of adolescents. Indeed,

as many as 70% of adolescent psychiatric inpatients engaging in NSSI reported a lifetime

history of at least one suicide attempt (Nock et al., 2006).

15

Overall, 67% of the female inpatient adolescents in the study by Nock et al. (2006)

met the criteria for a DSM-IV personality disorder. Although about half of the female

participants (52%) met criteria for BPD, a considerable amount of them also met criteria for

avoidant (31%) and paranoid (21%) personality disorders, respectively (Nock et al., 2006).

Anyhow, diagnosing personality disorders in adolescence is controversial (Jacobsen &

Gould, 2007). On the one hand, adolescence is a time of rapid change and development, and

personality disorders show substantial instability in adolescence (Mattanah, Becker, Levy,

Edell, & McGlashan, 1995). Thus, signs of personality disorders in adolescents may

accurately reflect current distress and dysfunction but they may not represent coherent,

differentiable syndromes with stability over time (Becker, Grilo, Edell, & McGlashan, 2000).

On the other hand, by ignoring possible personality disorders in this age group, many

adolescents may not receive appropriate psychological treatments (Miller, Muehlenkamp, &

Jacobsen, 2008). Indeed, some findings show that features of some personality disorders have

construct validity and can be reliably identified in adolescents (Ludolph et al., 1990).

Little is known of the underpinnings of NSSI (Lloyd-Richardson et al., 2007). Some

etiological factors are probably childhood trauma such as physical, emotional and sexual

abuse, neglect and separation (Gratz et al., 2002; Zorouglu et al., 2003), insecure attachment

(Gratz et al., 2002), dissociation (Gratz et al., 2002; Zoruglu, et al., 2003), undesirable life

events (Garrison et al., 1993) and biological vulnerabilities involving noradrenergic,

serotonergic, doperminergic and opiatergic abnormalities (Oquendo & Mann, 2000; Stanley et

al., 1992).

Research findings suggest a role for impulsivity in NSSI. Impulsivity can be defined

as the failure to resist an impulse, drive or temptation that is harmful to onself or others

(Cherkasky & Hollander, 1997). A majority of adolescents reports that their NSSI typically is

16

engaged in impulsively or with little forethought (Kumar, Pepe, & Steer, 2004; Lloyd-

Richardson et al., 2007; Nock & Prinstein, 2005). Also, NSSI is associated with heightened

levels of self-reported impulsivity (Ross, Heath, & Toste, 2009). Furthermore, lifetime

frequency of NSSI is positively correlated with impulse regulation difficulties (Ross et al.,

2009). However, these findings are exclusively based on self-reports. People may have only

little or no direct introspective access to higher order mental processes, such as those involved

in the initiation of behaviour (see Nisbett & Wilson, 1977, for a review). Thus, one might

question the accuracy of the adolescents’ subjective reports about impulsivity.

To address the question of why adolescents engage in NSSI, Nock and Prinstein

(2004) proposed a model of the functional processes that produce and maintain NSSI

behaviours. The model includes four primary functions of NSSI differing along two

dichotomous dimensions. First, NSSI is engaged in because it is automatically reinforcing

(e.g., to regulate emotions) and/or socially reinforcing (e.g., to regulate or alter one’s social

environment). Second, NSSI is engaged in because it is reinforced in a positive (i.e., followed

by a favorable stimulus) or negative manner (i.e., followed by the removal of an aversive

stimulus) (Nock & Prinstein, 2004). Automatic-negative reinforcement refers to engaging in

NSSI to reduce negative affective states (“ to stop bad feelings”). Automatic- positive

reinforcement involves engaging in NSSI to generate a desirable psychological state (“ to feel

something”). Social-negative reinforcement refers to engaging in NSSI to avoid or escape

from interpersonal task demands (“ to avoid doing something unpleasant”). Social-positive

reinforcement involves engaging in NSSI to gain attention from others or gain desirable

materials (“to let others know how unhappy I am”) (Nock & Prinstein, 2004).

Adolescents typically report several reasons for engaging in NSSI (Lloyd-Richardson

et al., 2007). A considerable number of both adolescent psychiatric patients (Nock &

17

Prinstein, 2004) and community sampled adolescents (Lloyd-Richardson et al., 2007) endorse

social-reinforcement functions of their NSSI. Although not completely consistent (Lloyd-

Richardson et al., 2007), reasons related to automatic reinforcement are nevertheless endorsed

most frequently both by adolescent psychiatric patients (Kumar et al., 2004; Nock &

Prinstein, 2004; Penn, Esposito, Schaeffer, Fritz, & Spirito, 2003) and community sampled

adolescents engaging in NSSI (Laye-Gindhu & Schonert-Reichl, 2005; Ross & Heath, 2003).

For instance, prior to engaging in NSSI, adolescents experience negative emotions, such as

anger, sadness and anxiety, which are reduced during and especially after having self-injured

(Laye-Gindhu & Schonert-Reichl, 2005; Ross & Heath, 2003). In sum, the bulk of the

research findings supports the emotion regulation hypothesis, stating that adolescents engage

in NSSI to regulate emotions, most often to decrease their negative affective states but

sometimes also to generate affective states (Jacobsen & Gould, 2007). However, these

findings are exclusively based on adolescents’ retrospective self-reports, which might be

questioned from a methodological perspective (Jacobsen & Gould, 2007). First, the

retrospective nature of the self-reports, asking the adolescents why they engaged in NSSI

several weeks or even months earlier, might be a threat to the reliability of the reports

(Jacobsen & Gould, 2007). Second, self-reports depend on the adolescents having enough

insight to consciously being aware of why they engage in NSSI (Jacobsen & Gould, 2007). As

referred to above, a majority of adolescents report that their NSSI typically is engaged in

impulsively or with little forethought (Kumar et al., 2004; Lloyd-Richardson et al., 2007;

Nock & Prinstein, 2005), suggesting that a substantial number of them might not be aware of

why they engage in NSSI.

18

Executive Functions in Emotion Regulation

Executive functions may be defined as the skills that are essential for purposeful, goal-

directed activity (Anderson, 1998). Converging evidence indicates that the prefrontal cortex is

central in executive functions (see Rogers et al., 2004, for a review). Although the different

executive functions are interrelated, they are meaningfully diverse abilities (Miyake et al.,

2000). Shifting between mental sets or tasks, updating and monitoring of information in

working memory, and inhibition of dominant responses, are main aspects of executive

functions (Miyake et al., 2000). Although the picture is not completely consistent (Herba,

Tranah, Rubia, & Yule, 2006), some find sex differences in executive functions in adolescents

(Anderson, Anderson, Northam, Jacobs, & Catroppa, 2001; Fields, Collins, Leraas, &

Reynolds, 2009). For instance, females performed generally better than males on tests

measuring set-shifting ability in a cross-sectional study investigating the development of this

ability from childhood into early adulthood (Kalkut, Han, Lansing, Holdnack, & Delis, 2009).

However, females and males showed differential developmental trajectories across ages.

Females showed a faster rate of improvement than males on a design fluency switching task

during adolescence until the 16-17 years age group at which point males’ performance

became greater than females’. On the other hand, on colour-word interference and verbal

fluency switching tasks, males showed a faster rate of improvement during early adolescence

than females (Kalkut et al., 2009).

In an empirically based model of the neural basis of emotion processing, two neural

systems underlie neuropsychological processes that are important for emotional behaviour

(Phillips, Drevets, Rauch, & Lane, 2003). The ventral system, including the amygdala, insula,

ventral striatum and ventral regions of the anterior cingulate gyrus and prefrontal cortex, is

primarily important for the identification of the emotional significance of a stimulus, the

19

ensuing production of an affective state, and the automatic regulation of emotional responses.

The dorsal system includes the hippocampus and dorsal regions of anterior cingulate gyrus

and prefrontal cortex. It is important for the performance of executive functions, which

includes effortful regulation of affective states and emotional behaviours. This involves an

inhibition or modulation of the processes that are mainly dependent upon the ventral system

(Phillips et al., 2003).

In accordance with this model, multiple lines of research findings suggest that

executive functions are relevant for emotion regulation. Several studies show that executive

functions are impaired in disorders characterized by abnormalities in emotion regulation, such

as depression (Harvey et al., 2004; see Rogers et al., 2004, for a review; Weiland-Fiedler et

al., 2004) and bipolar mood disorder (see Bearden, Hoffman, & Cannon, 2001, for a review;

Borkowska & Rybakowski, 2001). Furthermore, research findings show that individuals

lower in working memory capacity struggle more than others in regulating both their

emotional experiences and expressions (Schmeichel, Volokhov, & Demaree, 2008). By

loading working memory with tasks demanding effortful cognitive processing, mood-

congruent processing can be prevented and thereby result in distraction from negative moods

(Van Dillen & Koole, 2007). In this way working memory is one mechanism through which

distraction from negative moods operates (Van Dillen & Koole, 2007) and is thereby related

to emotion regulation. Another mechanism through which emotion regulation occurs, is

suppression (Nash et al., 2007). Although suppression does not provide relief from the

subjective experience of negative emotions, it can be adaptive by restraining emotional

expressive behaviours (Gross & Levenson, 1997). Specifically, unregulated emotional

expression and responding might have destructive effects, as in the abrupt expression of

anger, suggesting that in some circumstances the failure of withholding emotional expressions

20

might be problematic (Gross & Levenson, 1997). Importantly, suppression demands

inhibition of prepotent responses (Nash et al., 2007). Summing up, several lines of research

findings implicate that impaired executive functions might suggest an ineffective ability per

se to regulate emotions as well as emotional expressive behaviours.

The Neuropsychology of Self-Injurious Behaviours in General and NSSI in Particular

Only a few studies have examined neuropsychological functions in adolescents

engaging in self-injurious behaviours in general and NSSI in particular. To a large extent the

studies are based on the hypothesis that self-injurious behaviours may be associated with

frontal lobe function. Accordingly, the studies have primarily investigated neuropsychological

functions assumed to depend heavily on the frontal brain lobes. With one exception

(Oldershaw et al., 2009), no deficits in the investigated neuropsychological functions have

been found in adolescents engaging in self-injurious behaviours as compared with different

comparison groups (Dougherty et al., 2009; Janis & Nock, 2009; Ohmann et al., 2008).

Examining social and emotional self-regulation in adolescent females engaging in self-

injurious behaviours, no differences were found between adolescent females engaging in self-

injurious behaviours and adolescent females with none such behaviours on tests of executive

functions, i.e., the Stroop and the Wisconsin Card Sorting Test (Ohmann et al., 2008). No

differences were found between adolescents and adults engaging in NSSI as compared to

controls on behavioural measures of three different dimensions of impulsivity, i.e., the

Conners’ Continuous Performance Test (CPT), the Iowa Gambling Task (IGT) and a

computer-based measure of delay discounting (Janis & Nock, 2009). In contrast, Oldershaw et

al. (2009) found that adolescents who currently self-harmed, showed impaired decision

making, as measured by the IGT, as compared with adolescents with a previous history of

self-harm, adolescents with a depression and healthy controls. However, adolescents who

21

currently or previously self-harmed were not impaired on the Means-Ends Problem-Solving

Procedure, a measure of problem-solving skills (Oldershaw et al., 2009). As compared with

adolescents with a history of at least one suicide attempt and of NSSI behaviours, adolescents

with a history of NSSI only did not show elevated levels of impulsivity, as measured by the

Two Choice Impulsivity Paradigm and the GoStop Impulsivity Paradigm, measuring two

different dimensions of impulsivity (Dougherty et al., 2009).

Several methodological issues should be considered when reviewing these studies.

First, as evident when referring to the studies, different terms involving different definitions

of self-injurious behaviours have been used across studies. In two of the studies (Ohmann et

al., 2008; Oldershaw et al., 2009), a broader definition of self-injurious behaviours, than that

of NSSI, was used. Specifically, the definition included direct and indirect forms of self-

injuring behaviours with and without suicidal intent. Also, in one of the studies (Dougherty et

al., 2009), any direct or indirect non-fatal self-injuring act that was committed without

suicidal intent, was included in the definition of NSSI. Thus, as the studies have used different

definitions of self-injurious behaviours, they have not investigated the exact same phenomena.

This illuminates the parcity of studies investigating neuropsychological functions exclusively

in adolescents engaging in NSSI. Second, some of the adolescents in the self-injuring groups

and/or the comparison groups were drawn from clinical populations in all four studies

(Dougherty et al., 2009; Janis & Nock, 2009; Ohmann et al., 2008; Oldershaw et al., 2009).

Thus, different comorbid conditions in both the self-injuring and the comparison groups in the

studies might have influenced the findings, making it difficult to detect potential specific

impairments in neuropsychological functions in adolescents engaging in self-injurious

behaviours. Third, all of the studies only had one group of adolescents engaging in self-

injurious behaviours. As adolescents engaging in self-injury represent a heterogeneous group

22

(Lloyd-Richardson et al., 2007; Whitlock et al., 2008), potential differences between

subgroups of adolescents engaging in these behaviours and healthy controls, respectively,

might be impossible to detect when treating all adolescents engaging in self-injury as one

group. Fourth, to a considerable extent, the studies have used different tests of executive

functions, impulsivity, decision-making and problem-solving. Even though all tests used in

the studies are assumed to measure frontal lobe functions, they measure subtly different

aspects of frontal lobe functions and by no means they capture all neuropsychological

functions subserved by the frontal lobes. This emphasizes the need for conducting further

studies investigating a broader range of neuropsychological functions depending both on the

frontal lobes as well as on other brain structures, before establishing firm conclusions with

respect to the neuropsychological functioning of adolescents engaging in NSSI. For instance,

no previous studies have investigated verbal learning and memory in adolescents engaging in

NSSI.

In addition to these methodological considerations, yet another issue might be relevant

when considering the scarcity of neuropsychological findings supporting an association

between self-injurious behaviours and impulsivity in particular. Conceivably, adolescents

engaging in NSSI are impulsive only in certain contexts (Janis & Nock, 2009). It might be

that they impulsively engage in NSSI only when under extreme stress or in psychological

distress (Janis & Nock, 2009). Possibly, this might help explain why the majority of the

reviewed neuropsychological studies using performance-based measures of impulsivity have

not found elevated levels of impulsivity in adolescents engaging in self-injurious behaviours.

23

Serotonin in Self-Injurious Behaviours, NSSI, Emotion Regulation and Impulsivity

Although the picture is not completely consistent (Stanley et al., 2010), multiple lines

of evidence suggest that serotonin (5-hydroxytryptamine, 5-HT) is implicated in the

pathophysiology of self-injurious behaviour (McCloskey, Ben-Zeev, Lee, Berman, &

Coccaro, 2009a). Decreased 5-HT activity has been linked to self-harm in general (Steiger et

al., 2001) and NSSI in particular (Herpertz, Sass, & Favazza, 1997). Furthermore, selective

serotonin reuptake inhibitor (SSRI) has proven effective in reducing self-injury (Markovitz,

Calabrese, Schulz, & Meltzer, 1991). In adults with intermittent explosive disorder and in

healthy controls, experimentally lowered 5-HT enhanced self-injurious behavior, assessed by

a behavioural measure of self-aggression (McCloskey et al., 2009a). Peripheral serotonin

levels were lower in adolescents engaging in self-inflicted injury as compared with healthy

controls (Crowell et al., 2008). Again, different terms and definitions of self-injurious

behaviours are used in the studies. For instance, in three of the studies, self-injurious

behaviours encompassed both direct and indirect self-injurious acts with and without suicidal

intent (Crowell et al., 2008; McCloskey et al., 2009a; Steiger et al., 2001). This emphasizes

the need for further studies to investigate the association between serotonin functioning and

NSSI in particular. Still, the findings might suggest a role for serotonin in self-injurious

behaviours in general and NSSI in particular.

In addition to being associated with self-injurious behaviours in general and NSSI in

particular, reduced 5-HT neurotransmission plays an important role in impaired emotion

regulation (Canli & Lesch, 2007; Lesch, 2005; Walderhaug et al., 2007) as well as in impaired

impulse control (Dolan, Anderson, & Deakin, 2001; Linnoila et al., 1983; Walderhaug et al.,

2002, 2007). Indeed, abnormalities in 5-HT function in regions of the prefrontal cortex may

be especially important in impaired emotion regulation resulting in impulsive affective action

24

(Davidson, Putnam, & Larson, 2000). Possibly, the mechanism for the association between

NSSI, impaired emotion regulation, and the potential heightened level of impulsivity might

be found in lowered 5-HT function.

There are various subtypes of impulsivity (Evenden, 1999; Schmidt, 2003;

Winstanley, Dalley, Theobald, & Robbins, 2004), such as dimensions of impulsive action, or

the inability to inhibit a prepotent motor response or behavioural disinhibition (McCloskey et

al., 2009b; Winstanley et al., 2004), and cognitive impulsivity (McCloskey et al., 2009b;

Schmidt, 2003), such as reflection impulsivity (Morgan, Impallomeni, Pirona, & Rogers,

2005), impulsive decision making and impulsive choice (Winstanley et al., 2004). Low 5-HT

function seems particularly closely associated with increased impulsivity on behavioural

measures reflecting the dimension of impulsive action (Crean, Richards, & de Wit, 2002;

Walderhaug et al., 2002, 2007; Winstanley et al., 2004, but see Clark et al., 2005). NSSI is

associated with low 5-HT function, which in turn is closely linked to increased impulsive

action. Thus, NSSI might appear as a type of impulsive action rather than involving a type of

cognitive impulsivity.

25

Main Research Aims

Paper I

A primary aim of the study was to explore the main aspects of executive functions,

i.e., shifting, updating and inhibition, in adolescents engaging in NSSI. As adolescents

engaging in NSSI constitute a heterogeneous group, we examined a high-severity NSSI

group, a low-severity NSSI group in addition to a control group along these basic dimensions

of executive functions. As there may be sex differences in NSSI and executive functions, we

investigated the possible interactive of sex.

Paper II

Another main aim of the study was to explore verbal learning, recall, recognition and

intrusions in adolescents engaging in NSSI as compared with healthy controls. As females

outperform males in verbal learning and memory, we investigated the interactive effect of sex.

Paper III

The primary aims were to investigate the effects of an experimentally induced

lowering of serotonin, via acute tryptophan depletion (ATD), on impulsivity and mood in

female adolescents engaging in NSSI. It was hypothezised that the tryptophan-depleted girls

would show increased impulsive action and report lowered mood as compared with their

sham-depleted counterparts.

26

Materials and Methods

Design

The study consisted of three different sessions; a screening session, a test session and

an experimental session. In the test session, a comparative cross sectional design was used.

Neuropsychological functioning and clinical characteristics were assessed in adolescents

engaging in NSSI as compared with healthy controls. In the experimental session involving

ATD, a randomized double-blind placebo-controlled parallel group design was used. Female

adolescents engaging in NSSI were randomly assigned to either a tryptophan or a sham

depletion group, respectively. Performance on measures of impulsivity and mood was

compared between the respective tryptophan-depleted and sham-depleted female adolescents.

Neither the experimenters nor the participants were aware of the participants’ group status.

Participants and Procedures

The data included in the three papers in this thesis was collected from the same pool of

participants. The data reported and discussed in papers I and II was collected from the sample

selected from the screening session. The data reported and discussed in paper III was

collected from adolescents who were selected from the screening session and who had

participated in the test session. In paper I, data from 97 participants was included, in paper II,

data from 98 participants were included and in paper III, data from 32 participants were

included.

See figure 1 for the description of the participants in the three sessions of the study.

27

Figure 1. The participants in the three sessions of the study

327 adolescents were recruited and participated in the screening session

Paper I : NSSI group (n=62; 48 females, 14 males) and control group (n= 35; 25 females, 10 males)Paper II: NSSI group (n=62; 48 females, 14 males) and control group (n= 36; 26 females, 10 males)

74 adolescents in the NSSI group and 42 adolescents in the control group were selected for participation in the test session

62 adolescents (48 females, 14 males) in the NSSI group and 41 adolescents (30 females, 11 males) in thecontrolgroup participated in the test session Paper I and paper II: 5 adolescents (4 females, 1 male)

in the control group excluded from all data analysesPaper I: 1 additionaladolescent (female) in the controlgroup excluded from all data analyses

Adolescent opt out in NSSI group (n=12)Adolescent opt out in control group (n=1)

42 female adolescents in the NSSI group were convenience sampled for participation in the experimentalsession Adolescent opt out (n=2)

Parental opt out (n=1)Adolescents excluded from participation because ofSSRIs (n=2)

37 female adolescents in the NSSI group participated in the experimental session

Adolescents excluded from analyses because ofvomiting (n=4)Adolescents excluded from analyses because ofrefusing to ingest the mixture (n=1)32 female adolescents in the NSSI group were included in all data analyses from the experimental session

(Paper III)

17 high schools in Oslo and nearby boroughs agreed to participate

Seventeen high schools in Oslo and nearby areas agreed to participate in the study. All

Grade 9 students present at the schools at the scheduled times, were approached to participate

via classroom announcements. As will be described, one group of participants were seen only

in the screening session, a second group in the screening and test sessions, and a third group

in the screening, test and experimental sessions.

The screening session. A total of 327 adolescents were recruited and participated in

the screening session. Participants from each school completed a questionnaire on NSSI in a

classroom. NSSI was defined as the deliberate, direct destruction or alteration of body tissue

without suicidal intent. This excludes acts such as mentally hurting oneself and engaging in

risky behaviours. Inclusion in the NSSI group required having engaged in at least two

28

different NSSI behaviours during the past year, as assessed by their responses on the

questionnaire on NSSI. Group sizes of approximately 30 adolescents would enable us to

detect group differences in neuropsychological functions (Kyte, Goodyer, & Sahakian, 2005;

Matthews, Coghill, & Rhodes, 2008). To ensure such group sizes in the ensuing test session,

we screened until we had 74 adolescents meeting the criteria for inclusion in the NSSI group.

The control group comprised 42 adolescents matched as closely as possible on sex, ethnicity

and school belonging to the NSSI group, and had never engaged in any NSSI.

The test session. Ahead of the test session, 12 of the 74 adolescents in the NSSI group

and 1 of the adolescents in the control group withdrew from further participation. This left 62

adolescents (48 females, 14 males; typical age range 14-15 years) in the NSSI group and 41

adolescents (30 females, 11 males; typical age range 14-15 years) in the control group in the

test session. All participants met at the Department of Psychology at the University of Oslo.

They completed neuropsychological tests and questionnaires on clinical characteristics. A

clinical psychologist administered the sections covering some selected psychiatric diagnoses

in a semi-structured diagnostic interview. All participants were tested individually. Five

participants who had reported they had never engaged in NSSI on the screening questionnaire,

revealed in the interview that they had engaged in one NSSI behaviour during the past year.

They were excluded from all analyses as they failed to meet the criteria for any of the groups,

this left 36 adolescents (26 females, 10 males; typical age range 14-15 years) included in the

control group. Due to extreme scores on several measures on the executive functions tests,

one girl in the control group was excluded from all the analyses as reported in paper I.

With respect to all analyses as reported in paper I, based on participants’ reported

NSSI in the screening questionnaire and in the section on NSSI in the diagnostic interview,

participants were classified into three groups: a high-severity NSSI group (n=33), a low-

29

severity NSSI group (n= 29) and a control group (n=35). Participants meeting the initial

criteria for inclusion in the NSSI group, were given a score reflecting the severity of their

NSSI. Two NSSI characteristics were used to calculate the NSSI severity score; the form(s)

and the total number of different NSSI behaviours engaged in. With respect to NSSI forms,

NSSI behaviours were classified into three groups based on their potential for causing tissue

damage (Skegg, 2005; Whitlock et al., 2008). Behaviours with potential for superficial tissue

damage were each scored 1, while those with potential for causing bruising or light tissue

damage were each scored 2. Lastly, behaviours with potential for causing severe tissue

damage, were each scored 3. To ensure reliability of the classification of NSSI behaviours

into the three groups, training of two raters was completed, resulting in 90% agreement on

20% of the data. Thus, for each participant meeting the initial criteria for inclusion in the

NSSI group, the weighted scores of the NSSI behaviours were summarized to give a NSSI

severity score (M=7.9, S.D.=3.6, Median=7.0). The median was used as the cut off point

separating the participants into the two NSSI subgroups. Nine participants scored this value.

Five were classified into the high-severity NSSI group as they had engaged in NSSI

behaviours in all three NSSI groups, a similar pattern to the majority (i.e., 25 of 28) of

participants in the high-severity NSSI group. The four remaining participants were classified

into the low-severity NSSI group as they had engaged in NSSI behaviours in two NSSI

groups, either group 1 and 2 or group 1 and 3, a similar pattern to the majority (i.e., 20 of 25)

of participants in the low-severity NSSI group.

The experimental session. Inclusion in the experimental session (involving ATD)

required that the female adolescents had engaged in minimum two different NSSI behaviours

during the past year. Forty-eight female adolescents met the inclusion criteria and 42 of them

were convenience sampled and included for participation. After the test session (conducted 3

30

to 32.9 weeks; mean 17.7 weeks, prior to the experimental session) 3 participants withdrew

from further participation. Two participants were using SSRIs and were excluded from further

participation. Four participants vomited in response to the amino acid mixture and one

participant refused to ingest the amino acid mixture, and their data were excluded from all

statistical analyses. The remaining 32 participants completed the whole experiment and were

included into all analyses.

ATD was achieved through a mixture of amino acids devoid of tryptophan as

described previously (Zepf et al., 2008). The ingredients of the liquid mixtures in both

conditions were consistent with the receipts used with children and adolescents in a previous

study (Zepf et al., 2008). It was dosed according to bodyweight, and contained the following

amount of amino acids per 10 kg: L-phenylalanine 1.32 g, L-leucine 1.32 g, L-iso-leucine

0.84 g, L-methionine 0.5 g, L-valine 0.69 g, L-threonine 0.6 g and L-lysine 0.96 g. During

sham depletion, the mixture also contained L-tryptophan (0.70 g per 10 kg) (Zepf, Wöckel,

Poustka, & Holtmann, 2009).

The amino acids were mixed with 200 ml cold water, 10 ml chocolate syrup and 3

drops of citric essence. Participants were offered protein-free sweets and juices to ease the

ingestion of the mixture, and were encouraged to swallow it as fast as possible to avoid the

unpalatable taste. Participants’ guesses of whether they had been in the active or placebo

condition were no better than chance, with 25.8% of the participants guessing they had been

in the placebo condition.

Participants and their parents received written and oral information, telling the

participants to take low protein food the day before participation, to abstain from any food

containing proteins after 8:00 pm the day before participation, and to fast from the morning at

the study day. The session started at about 8:00 a.m. Following the collection of baseline

31

blood samples, the participants completed a questionnaire on mood. The amino acid mixtures

were then given to the participants. During a four and a half hour long waiting period,

participants read, socialized or watched emotionally neutral movies, always together with an

experimenter. They were told not to sleep or eat anything but water, protein-free juices and

sweets provided by the experimenter.

To prevent a lack of Nicotine-adenine dinucleotide (NAD, a tryptophan-derived

vitamin) because of depletion, B-tonin, a drink of B vitamins, was administered one hour after

the ingestion of the amino acid mixture. Two hours after the ingestion of the amino acid

mixture, participants were each offered an apple. A second blood sample was collected at

about 4, 5 hours after ingesting the amino acid mixture. The participants then performed the

behavioural measures of impulsivity and completed the questionnaire on mood a second time.

Participants were tested individually in separate rooms and during the debriefing they were

given a protein-rich meal.

Behavioural and Clinical Measures

Clinical measure in the screening session.

The Functional Assessment of Self-Mutilation (FASM). To measure NSSI we

administered the FASM (Lloyd, Kelley, & Hope, 1997 as cited in Lloyd-Richardson et al.,

2007), a self-report questionnaire of the methods, frequency and functions of NSSI. The

FASM has been used in studies of community and psychiatric samples of adolescents, which

have yielded support for its psychometric properties (Guertin et al., 2001; Lloyd-Richardson

et al., 2007; Nock & Prinstein, 2004, 2005). For instance, the concurrent validity of the FASM

is supported by its significant associations with measures of depression (Guertin et al., 2001;

Nock & Prinstein, 2005), current suicide ideation (Lloyd-Richardson et al., 2007) past suicide

32

attempt (Guertin et al., 2001), recent suicide attempt and hopelessness (Nock & Prinstein,

2005). A Norwegian version of the FASM was used. The translation of the FASM into

Norwegian was performed by Fikke in cooperation with a bilingual person, with English as

native language.

Clinical measures in the test session.

The Beck Depression Inventory (BDI). Depressive symptoms were measured with the

BDI (Beck, Steer, & Garbin, 1988), a 21 item self-report measure of affective, behavioural,

cognitive, and somatic symptoms of depression. Estimates of internal consistency reliability

have ranged from 0.79 to 0.91 in samples of both community and outpatient adolescents

(Adewuya, Ola, & Aloba, 2007; Ambrosini, Metz, Bianchi, Rabinovich, & Undie, 1991;

Larsson & Melin, 1990; Marcotte, Alain, & Gosselin, 1999; Teri, 1982), while test-retest

reliability have ranged from 0.74 to 0.98 depending on the time intervals between testing

(Ambrosini et al., 1991; Larsson & Melin, 1990). The BDI shows good convergent and

discriminant validity in adolescent samples of psychiatric hospital inpatients and high school

students (Barrera & Garrison-Jones, 1988).

The Beck Anxiety Inventory (BAI). Anxious symptoms were assessed with the BAI, a

21-item self-report measure of anxiety, specifically developed to reliably discriminate anxiety

from depression (Beck, Epstein, Brown, & Steer, 1988). In both community and clinical

samples of adolescents, estimates of internal consistency reliability have ranged from 0.88 to

0.94 (Jolly, Aruffo, Wherry, & Livingston, 1993; Osman et al., 2002). Among inpatient

adolescents, BAI shows moderate to high convergent validity (Jolly et al., 1993). The BAI

total score seems sensitive to levels of anxiety severity reported by clinical and non-clinical

adolescents (Osman et al., 2002).

33

The State-Trait Anger Expression Inventory (STAXI). The experience of anger (both

state and trait anger) and the expression of anger (anger directed inward and outward as well

as attempts to control anger) were measured using the STAXI (Spielberger, 1988). It consists

of 44 items that are rated on 4-point Likert scales, with higher scores indicating greater

intensity or frequency of experienced or expressed anger. Adequate internal consistency and

construct validity have been reported for the subscales of this inventory (Spielberger, 1988),

which has been used with adolescents (Guertin et al., 2001; Lehnert, Overholser, & Spirito,

1994). A Norwegian adaptation of the STAXI, that is found to have quite similar

psychometric properties and factor structure as those of the original American version

(Håseth, 1996), was used.

Kiddie-Sads-Present and Lifetime Version (K-SADS-PL). To investigate the presence

of psychiatric diagnoses, the K-SADS-PL (Kaufman et al., 1997) was administered by a

clinical psychologist. It is a semi-structured diagnostic interview assessing current and

lifetime history of psychopathology in children and adolescents according to criteria from the

DSM-IV (American Psychiatric Association, 1994). The K-SADS-PL has demonstrated high

inter-rater agreement (range: 93% to 100%), good to excellent test-retest reliability kappa

coefficients (0.63-1.00), and its concurrent validity is supported, as evidenced by associations

with self-report scales (Kaufman et al., 1997). The following diagnoses were considered

particularly relevant and were examined: MDD, Generalized Anxiety, Obsessive Compulsive

Disorder, Panic Disorder, Social Phobia, PTSD, Anorexia Nervosa, Bulimia Nervosa,

Attention Deficit Hyperactivity Disorder (ADHD), Alcohol Abuse and Substance Abuse.

Neuropsychological measures in the test session.

Wechsler Abbreviated Scale of Intelligence (WASI). WASI (Psychological

Corporation, 1999) provides a brief estimate of intelligence. It consists of four subtests:

34

Vocabulary, block design, similarities, and matrix reasoning. The WASI has excellent

reliability and stability (Strauss, Sherman, & Spreen, 2006). Reliability coefficients are .96,

.96 and .98 for the Verbal IQ (VIQ), Performance IQ (PIQ) and Full-Scale IQ (FSIQ),

respectively (Strauss et al., 2006). The concurrent validity of the WASI is supported by

findings showing a significant correlation (r=.89) between the WASI FSIQ score and the

Kaufman Brief Intelligence Test Composite IQ score (Hays, Reas, & Shaw, 2002).

To measure each of the main aspects of executive functions, i. e., shifting, updating

and inhibition (Miyake et al., 2000), we selected three tests from the Cambridge

Neuropsychological Test Automated Battery (CANTAB; Cambridge Cognition, 2006). This

is a widely used tool for assessing neuropsychological functions (Kyte et al., 2005) and the

different CANTAB tasks are sensitive to neuropsychological impairments in a variety of

populations (see Strauss et al., 2006, for a review). Tests from the CANTAB have been

successfully employed in several adolescent populations (De Luca et al., 2003; Kyte et al.,

2005; Matthews et al., 2008). The three tests were as follows:

The Intra/Extradimensional (IED) Set Shift . We administered the IED Set Shift

(CANTAB; Cambridge Cognition, 2006) to measure the shifting aspect of executive

functions. The subject must learn which of two presented stimuli is correct, assisted by

feedback from the computer. Initially, two stimuli of one dimension (pink shapes) are shown,

then each of two dimensions (pink shapes and white lines) are shown. The stimuli and/or rules

change after six consecutive correct responses (the criterion of learning at each stage). These

shifts are initially intradimensional (pink shapes are the relevant dimension), then

extradimensional (white lines become the relevant dimension). The test terminates if at any

stage the subject fails to reach the criterion of learning after 50 trials. The variables of interest

were Stages completed, Pre-ED errors and EDS errors, reflecting the number of stages

35

completed successfully, the number of errors made prior to the extra-dimensional shift and in

the extra-dimensional stage of the task, respectively.

Figure 2. The IED Set Shift Test

The Spatial Working Memory (SWM) Test. We measured the updating aspect of

executive functions with the SWM test (CANTAB; Cambridge Cognition, 2006).

Specifically, this test measures updating and monitoring of spatial information in working

memory. The screen displays a number of boxes. The subject has to find one token in each

box and use them to fill up a column on the side of the screen. Gradually, the number of boxes

increases from three to eight. Touching any box where a token has already been found is an

error. The subject decides the order in which boxes are visited. The variables of interest were

Total errors and Strategy, reflecting the number of errors made and the use of an efficient

strategy for completing the task, respectively.

Figure 3. The Spatial Working Memory Test

36

The Stop Signal Task (SST). The SST (Logan, Cowan, & Davis, 1984) is also part of

the CANTAB (Cambridge Cognition, 2006) and was administered to measure the inhibition

aspect of executive functions. Specifically, this test measures inhibition of dominant

responses. The screen shows a white ring, in which a left-or right pointing arrow is displayed.

First, the subject has to press the left button on a press pad when seeing a left-pointing arrow,

and the right button when seeing a right-pointing arrow. In the second part of the task, the

subject has to continue pressing the buttons as before, but has to withhold pressing the button

if hearing a beep. The variables of interest were Direction errors on stop and go trials and

Stop Signal Reaction Time (SSRT) last half, expressing the number of times the subject

pressed the wrong button and the time between the stop signal and the inhibition of the

response, respectively (Eagle et al., 2007; Logan & Cowan, 1984). A model accounts for

response inhibition in the stop-signal paradigm in terms of a “horse race” between two sets of

processes, one that generates a response for the primary task and one that responds to the stop

signal (Logan & Cowan, 1984). If the primary-task process finishes before the stop-signal

process, the response is executed, but if the stop-signal process finishes before the primary-

task process, the response is inhibited (Logan & Cowan, 1984). Research findings (De Jong,

Coles, Logan, & Gratton, 1990) support a major assumption underlying the horse race model,

namely that the respective primary-task and stopping processes are independent (Logan &

Cowan, 1984).

Figure 4. The Stop Signal Task

37

Children’s Auditory Verbal Learning Test-2 (CAVLT-2). The CAVLT-2

(Psychological Assessment Resources, 1993) was administered to measure auditory verbal

learning and memory. In the first free-recall word list, 16 words are presented to be

remembered, followed by immediate recall. This is repeated for five trials. A sum score of

correctly recalled words in trials 3, 4 and 5 comprises level of learning. In the interference

trial, a second free-recall word list, the interference list, composed of 16 new words, is

presented to the subject who immediately recalls as many words as possible from this list.

Immediate memory span is computed by adding correctly recalled words in trial 1 of the first

list and correctly recalled words in the interference list. Immediately following recall of the

interference list, the individual is asked to recall words only from the first list, constituting the

immediate recall trial. After 15 to 20 minutes the individual is again asked to recall words

from the first list, representing the delayed recall trial. Lastly, the recognition list is read to

the individual. All words from the first list, half of the words in the interference list and eight

new words are included. Following the presentation of each word, the individual is asked to

say “yes” if the word was in the first list and “no” if it was not, comprising the recognition

accuracy score. Total intrusions are the sum score of incorrectly recalled words throughout

all trials except the recognition trial. Three variables were computed to investigate loss of

information between the learning phase and immediate and delayed recall and between

immediate and delayed recall. The first was computed by subtracting the immediate recall

score from the level of learning score, the second by subtracting the delayed recall score from

the level of learning score, and the third by subtracting the delayed recall score from the

immediate recall score. In a study with adolescents, findings have yielded support for the

validity of the results from the CAVLT-2 (Talley, 1993). For instance, scores on the

38

immediate memory span was significantly correlated with reading and scores on the delayed

recall was significantly correlated with mathematics, supporting the convergent validity of the

results from the CAVLT-2 (Talley, 1993).

Behavioural measures in the experimental session.

The Continuous Performance Test, Identical Pairs Version (CPT-IP). We

administered the CPT-IP (Cornblatt, Risch, Faris, Friedman, & Erlenmeyer-Kimling, 1988) to

measure impulsive action. Four- digit numbers and nonsense shapes are visually presented in

two trials. Each stimulus appears on the screen for 50 msec, presented at a constant rate of one

per second. The subject’s task is to respond as fast as possible whenever two identical stimuli

are presented in a row. A correct identification of a matching set is called a “hit,” while a

response to a stimulus similar, but not identical to the preceding stimuli is called a “false

alarm.” Based on hits and false alarms, signal detection indices (e.g., β and d’) are calculated.

The β value is a measure of response style and captures subjects’ tendency to over- or

underrespond in situations with competition between behavioural suppression and active

responding (Cornblatt et al., 1988; Walderhaug, Herman, Magnusson, Morgan, & Landrø,

2010). Lower β values, reflecting over- responding, indicate an impulsive response style

(Conners, Epstein, Angold, & Klaric, 2003), and are related to ADHD symptoms (Epstein et

al., 2003). Higher β values reflect a more cautious response style (Strauss et al., 2006) and are

associated with depression (Johnson & Magaro, 1987). The d’ is a measure of sensitivity or

discriminability and involves the participant’s sensory capability (Rutschmann, Cornblatt, &

Erlenmeyer-Kimling, 1977) and attentional capacity (Cornblatt & Malhotra, 2001). The

higher the score the better the performance (Rutschmann et al., 1977).

The Matching Familiar Figures Test (MFF20). To measure reflection impulsivity,

we administered the MFF20 (Cairns & Cammock, 1978). This test consists of 20 test items.

39

Following the administration of two practice items, the subject is shown a picture of an object

and six similar stimuli, of which only one is identical to the object (Kagan, Pearson, & Welch,

1966). The subject is asked to select the stimulus that is identical to the object (Kagan et al.,

1966). The primary variables of interest were the mean latency to first response, the total

number of errors committed, and the impulsivity or “I” score, which was calculated by

subtracting the standard score of the mean latency to first response from the standard score of

the total number of errors committed (Ze – Z1) (Salkind & Wright, 1977). The usefulness of

the MFF20 with adolescents is supported by findings showing moderate stability for the

latency, error and “I” scores respectively, as well as a high negative latency-error correlation

(Messer & Brodzinsky, 1981).

The Profile of Mood States (POMS). To measure the effect of ATD on mood, we

administered the POMS (McNair, Lorr, & Droppleman, 1971). It consists of 65 adjectives and

the subject’s task is to indicate how he/she feels at that moment by rating the degree to which

his or her current mood state corresponds to the respective adjectives. The intensity of each

mood adjective is rated from “not at all” to “extremely” on a 5-point Likert scale. Two total

mood disturbance (TMD) scores were calculated by adding the sum scores for all the

subscales of the POMS (i.e., tension-anxiety, depression-dejection, anger-hostility, vigor-

activity, fatigue-inertia, and confusion-bewilderment; weighting vigor-activity negatively), at

baseline and six hours after the ATD, respectively. To assess mood change, a mood change

variable was calculated by subtracting the TMD score at baseline from the TMD score six

hours after intake of the amino acids. The internal consistency reliability is .84 or greater for

the six POMS scales (Spielberger, 1972). The validity of the POMS for the measurement of

transitory mood states have been questioned (Spielberger, 1972). However, the POMS has

repeatedly been used in studies investigating mood effects of ATD (see Mendelsohn, Riedel,

40

& Sambeth, 2009, for a review), and importantly has been able to capture mood effects of

ATD (Walderhaug et al., 2007).

Assessment of Plasma Tryptohan Concentration in the Experimental Session

The analysis of total tryptophan was performed using a Biochrom 30 amino acid

analyzer (Biochrom Ltd., England). This system uses ion exchange chromotagraphy with

lithium buffers, post-column ninhydrin derivatization and photometric detection at

wavelength 570 nm. Prior to analysis of total tryptophan, plasma samples were deproteinized

by sulfosalicyclic acid. In the amino acids separation, a series of buffer solutions were run

through a column using cation exhange resin, containing the amino acids in solution. The

amino acids were then derivatizated, reacting with ninhydrin and detected at wavelength

570nm. An external standard (Sigma-Aldrich) was used for calibration.

Statistical Analyses

The Statistical Package for the Social Sciences (SPSS) for Windows (version 16.0 and

18.0; Inc., Chicago, IL, USA) was used to register and analyze all data. As reported in all

three papers, one-way between-groups analyses of variance (ANOVAs) were completed to

assess group differences in continuous demographic and psychometric variables. Group

comparisons in frequencies of each diagnosis scored as 0 (not present) or 1 (present) were

performed using chi-square tests. In instances of group differences in frequencies of

diagnoses, one-way ANOVAs were conducted to explore the main effects of each of the given

diagnoses (present versus not present) on the mean Z score of the variables on each executive

function test (paper I) and on scores of each learning and memory variable (paper II). In

instances of main effects of the given diagnoses on any of the neuropsychological variables,

the given diagnoses were included as additional fixed factors in further analysis investigating

41

the effect of group (NSSI group(s) versus control group) only on the specific

neuropsychological variables in which the preliminary analyses revealed main effects of the

given diagnoses.

Paper I. Scores on the dependent variables on the three tests of executive functions

were converted to Z scores. In doing so, we were able to make mean Z scores, reflecting the

mean scores of the variables on each executive function test for each participant; one for the

IED test variables, one for the SWM test variables and one for the SST variables. When

positive scores on the dependent variables on the executive function tests had opposite

meanings in their interpretation, some of them were reversed accordingly.

Two-way between-groups ANOVAs were performed to explore the main effects of

group (control group, low severity NSSI group, high severity NSSI group) and sex and their

possible interaction effects on the mean Z score of the variables on each executive function

test. Only when these initial analyses yielded significant effects, further two-way ANOVAs

with scores on each variable on the relevant executive function test as the dependent

variables, were completed. When interaction effects between group and sex were found, post-

hoc comparisons were performed using a dummy variable with six values representing the six

possible combinations of group and sex (3*2). All post-hoc comparisons were performed

using the Fisher's Least Significant Difference test.

Paper II. Two-way ANOVAs were completed to explore the main effects of group

(NSSI versus control) and sex, and their interaction effects on scores of each learning and

memory variable. When interaction effects between group and sex were found, post-hoc

comparisons were performed using a dummy variable with four values representing the four

combinations of group and sex (2*2). All post-hoc comparisons were applied using

Bonferroni corrections.

42

Paper III. We employed one sample t-tests to assess the effects of ATD and sham

depletion on plasma tryptophan concentrations. One-way ANOVAs were performed to assess

the effects of group (active depletion versus sham depletion) on the impulsivity measures and

on the mood change variable, respectively.

Ethical Considerations

The study was carried out in accordance with the Helsinki Declaration and approved

by the Regional Committee for Medical Research Ethics (REK sør-øst) and the Norwegian

Social Science Data Services (NSD). A researcher met all potential participants in their

classrooms, informing them about the study. The adolescents also received written

information, including one to their parents. Before participation, all participants and their

parents signed informed consents. Still, the study raises some ethical issues.

First, without doubt the use of the self-report questionnaires and the diagnostic

interview would reveal that some of the adolescents engaged in NSSI and/or had

psychological problems. Indeed, this clinical assessment could reveal that some of the

adolescents even met the criteria for one or several mental disorders. Thus, the research team

developed a thorough plan to ensure that participants who revealed that they were struggling

and were in need of help, would be followed up adequately. In brief, a network comprising

the research team, the school health services, the local mental health services and two clinical

psychologists, was established. Before we commenced the study, all the above mentioned

were contacted and informed about the study. In the screening session, all participants were

given oral and written information about the health service associated to their school, which

they could contact if needed. Also, after the screening session all schools were contacted by

the research team to get to know whether there had been any reactions of any kind among the

participants in response to having completed the questionnaire on NSSI. Throughout all the

43

study sessions, the most suitable unit within the established network was contacted by the

research team and hence made available for participants in need of professional help. In more

serious cases, such as severe depression or social problems, needing a referral to the local

mental health services, parents were informed. This was always in colloboration with the

participants.

Second, the participants would not necessarily have a direct benefit from the results of

any of the study sessions. Still, the results might come to the benefit of other adolescents at a

later time. Also, in instances where professional help was needed, study results for the

individual participant was provided if asked for.

Third, the experimental session involved the use of ATD. In brief, ATD presupposes

fairly strict rules regarding food intake the day before the study followed by fasting on the

actual study day. In addition, although no serious side effects have been reported, there have

been a few cases of nausea, vomiting and diarrhoea in response to ATD (see Moore et al.,

2000, for a review; Young, Smith, Pihl, & Ervin, 1985). Thus, exposing adolescent

participants to ATD involving fasting and potential uncomfortable side effects, represent an

ethical issue.

However, ATD is described as a safe method as its effects are rapidly reversed by

consuming a normal diet (Bell, Hood, & Nutt, 2005). In accordance with this, all participants

were served a high-protein meal immediately after having completed all the behavioural tests.

Furthermore, ATD is a well-known method that has been used in several studies with healthy

and various clinical samples (see Moore et al., 2000, for a review). A modified version of

ATD in which the amount of amino acids to be ingested are dosed according to the

participants’ body weight, have been developed specifically for research with children and

adolescents (Zepf et al., 2008). In a previous study using this modified version of ATD with

44

male children and adolescents with ADHD, no side effects were reported (Zepf et al., 2008).

Nevertheless, as no previous studies had been conducted with female adolescents engaging in

NSSI, an experimenter was always together with the participants in case of any unforeseeen

reactions to the depletion. Importantly, ATD makes it possible to study the effects on

impulsivity and mood of decreased serotonin neurotransmission in humans (Delgado et al.,

1990). Such experimental studies are essential to gain further knowledge on causal

relationships that might be involved in for instance NSSI. Thus, by using this method one

might gain important, novel knowledge which can come to the benefit of other adolescents at

a later time.

45

Results

Paper I

There were no significant group differences in sex ratios or on any IQ indicators. No

significant group differences were found in frequencies of any diagnoses with the exception

of current MDD [control group=0%, low-severity NSSI group=10.7%, high-severity NSSI

group=21.2%, χ2=8.19, df=2, p<.02] and previous MDD [control group=0%, low-severity

NSSI group=0%, high-severity NSSI group=15.2%, χ2=10.22, df=2, p<.01]. No main effects

of either current or previous MDD on the mean Z scores of the IED variables, the SWM

variables or the SST variables, respectively, were found. Thus, they were not included into

further analyses.

No significant group or sex differences or any interaction effect between group and

sex were found on the mean Z score of the IED variables.

On the mean Z score of the SWM variables, there were significant group differences

[F(5, 91)=3.98, p=.02, η2=.08]. There were no significant sex difference or interaction effect

between group and sex. Post-hoc comparisons revealed no significant group differences.

Significant group differences were found on the SWM Total error score [F(5, 91)=4.08,

p=.02, η2=.08] but no sex difference was found. There was a trend towards a significant

interaction effect between group and sex [F(5, 91)=2.75, p=.07, η2=.06]. A scatter plot

inspection of these results revealed that the significant main effect of group was caused by the

interaction effect of sex. Post-hoc comparisons showed that males in the high-severity NSSI

group had a higher score than both males (p=.00) and females in the control group (p=.03).

On the SWM Strategy score, there were significant group differences [F(5, 91)=3.52, p=.03,

η2=.07]; the high-severity NSSI group had a higher score than the low-severity NSSI group

(p=.04). No significant sex difference or interaction effect between group and sex emerged.

46

On the mean Z score of the SST variables, there were significant group differences

[F(5, 91)=6.26, p=.00, η2=.12]; the low-severity NSSI group had higher scores than the

control (p=.02) and the high-severity NSSI group (p=.01), respectively. A trend towards a sex

difference [F(5, 91)=3.91, p=.05, η2=.04] was found, while no interaction effect between

group and sex emerged. On the score on SST Direction errors on stop and go trials, there were

significant group differences [F(5, 91)=4.61, p=.01, η2=.09]; the low-severity NSSI group had

a higher score than the control group (p=.03). There were no sex difference or interaction

effect between group and sex. There were significant group differences on the score on the

SSRT variable [F(5, 91)=6.21, p=.00, η2=.12]; the low-severity NSSI group had a higher

score than the high-severity NSSI group (p=.00). A trend towards a sex difference emerged

[F(5, 91)=3.71, p=.06, η2=.04], while no interaction effect between group and sex was found.

Paper II

There were no significant group differences in sex ratios or on the IQ score. No

significant group differences were found in frequencies of any diagnoses except for current

MDD [control group=0%, NSSI group=16.4%, χ2=6.58, df=1, p=.01]. There were no effects

of current MDD on any of the learning and memory scores without on the level of learning

score [F(1,95)=4.74, p=.03, η2=.05]; those meeting the criteria for current MDD had lower

scores than those without current MDD. Thus, current MDD was included into further

analysis on the level of learning score only.

On the level of learning score, there was a significant group difference [F(3,94)=9.06,

p=.00, η2=.09]; the NSSI group had a lower score than the control group. No sex difference or

interaction effect between group and sex was found. Current MDD was included as an

additional independent variable into the analysis of the effect of group on the level of learning

47

score. The effect of current MDD disappeared, while there still was a trend towards a

significant effect of group on level of learning [F(2,94)=3.76, p=.06, η2=.04].

On the interference trial, no significant group difference or interaction effect between

group and sex were found. There was a significant sex difference [F(3,94)=5.53, p=.02,

η2=.06]; the males had a lower score than the females.

On the immediate memory span score, there was a significant group difference

[F(3,94)=4.92, p=.03, η2=.05]; the NSSI group had a lower score than the control group. No

significant sex difference or interaction effect between group and sex was found.

There were significant group differences on the immediate recall trial [F(3,94)=6.87,

p=.01, η2=.07]; the NSSI group had a lower score than the control group. No sex difference

was found, while there was a significant interaction effect between group and sex

[F(3,94)=10.53, p=.00 η2=.10]. Post-hoc comparisons showed that males in the NSSI group

had a lower score than males in the control group (p=.01). A scatter plot inspection of these

results revealed that the significant main effect of group was caused by the inferior

performance of the males in the NSSI group. On the delayed recall trial, there were significant

group differences [F(3,94)=5.20, p=.03, η2=.05]; the NSSI group had a lower score than the

control group. There was no sex difference, while there was a significant interaction effect

between group and sex [F(3,94)=5.95, p=.02 η2=.06]. Post-hoc comparisons revealed that

males in the NSSI group had a lower score than males in the control group (p=.04). A scatter

plot inspection of these results revealed that the significant main effect of group was caused

by the inferior performance of the males in the NSSI group. On the recognition accuracy

score, no significant sex or group difference was found, while there was a significant

interaction effect between group and sex [F(3,94)=5.74, p=.02, η2=.06]. Post-hoc comparisons

revealed that males in the NSSI group scored lower than females in the NSSI group (p=.01).

48

No significant group or sex differences or any interaction effect between group and

sex were found on the total intrusions score, the scores reflecting loss of information between

the learning phase and immediate and delayed recall, respectively, or between immediate and

delayed recall.

Paper III

As expected, ATD significantly decreased plasma concentrations of total tryptophan

(t(16) = -19.2, p<.000). Following ATD, the average decrease in total tryptophan level, was

78.9%. Sham depletion significantly increased plasma concentrations of total tryptophan

(t(14) = 7.8, p<.000). The average increase in total tryptophan level was 276.6% following

sham depletion.

There were no significant differences between the respective active depletion and

sham depletion groups in age, on any of the IQ scores or in frequencies of any of the

psychiatric diagnoses.

In the number mode of the CPT-IP, ATD had a statistically significant effect on the β

score (F(1, 30)=8.73, p=.01); the active group had a lower β score as compared with the

placebo group. Furthermore, ATD had a statistically significant effect on the d’ score (F(1,

30)=5.66, p=.02); the active group had a higher d’ score than the placebo group. ATD had a

statistically significant effect on the hit score (F(1,30)=5.37, p=.03); the active group had a

higher hit score than the placebo group. However, no ATD effect was found on the false

alarm score. In the shapes mode of the CPT-IP, ATD had no statistically significant effects on

the β, d’, hits or false alarms scores, respectively.

49

ATD had no statistically significant effects on any of the scores on the three MFFT

variables, ie. on the mean latency to first response, on the total number of errors committed,

or on the “I” score. Also, ATD had no effect on the mood change score.

50

Summary of Papers

Paper I

Background. The aim of this study was to investigate three main aspects of executive

functions (EFs), i.e. shifting, updating and inhibition, in adolescents engaging in non-suicidal

self-injury (NSSI) as compared with healthy controls. Method. EFs were assessed using the

Intra/Extradimensional Set Shift, the Spatial Working Memory (SWM) Test and the Stop

Signal Test (SST) from the Cambridge Neuropsychological Test Automated Battery

(CANTAB), in a high-severity NSSI group (n=33), a low-severity NSSI group (n=29) and a

healthy control group (n=35). Diagnostic characteristics were examined using the Kiddie-

Sads-Present and Lifetime Version. Results. There were group differences on the SWM Test.

A trend towards an interaction effect of sex revealed that males in the high-severity NSSI

group made significantly more errors than males and females in the control group.

Both males and females in the high-severity NSSI group made poor use of an efficient

strategy in completing the test. The low-severity NSSI group performed poorly on the SST,

making more errors than the control group and showing an impaired ability to inhibit initiated

responses, as compared with the high-severity NSSI group. There were group differences in

frequencies of current and previous major depressive disorder. However, no effects of these

diagnoses were found on any of the EF tests. Conclusions. This study demonstrates that NSSI

subgroups have distinct deficits in EFs. The high-severity NSSI group has working memory

deficits, while the low-severity NSSI group has impaired inhibitory control. This supports the

emotion regulation hypothesis.

Paper II

Background. To obtain further knowledge on the neuropsychological correlates of

non-suicidal self-injury (NSSI), various aspects of verbal learning and memory were

51

investigated in adolescents engaging in NSSI as compared with healthy controls. Method.

Verbal learning and memory was assessed using the Children’s Auditory Verbal Learning

Test-2 in a NSSI group (n=62) and a healthy control group (n=36). Results. The NSSI group

performed below the control group on measures of immediate memory span and level of

learning. Although males in the NSSI group had impaired recall and recognition, they

remembered most of what they learned. No group differences were found on the intrusion or

the interference measure. Conclusions. Adolescents engaging in NSSI exhibit impairments in

verbal learning and memory. The core problems involve impaired short-term

memory/working memory and difficulty in the encoding of material into long-term memory.

This suggests that an inefficient network comprising frontal cortex and more posterior

structures are involved in NSSI. Furthermore, the findings might be seen as a first reasonable

step in investigating whether adolescents engaging in NSSI may need training to improve

their verbal learning and memory, which in turn might affect their academic attainments.

Paper III

Background. Non-suicidal self-injury (NSSI) has repeatedly been associated with

impaired emotion regulation and impulsivity. Low serotonin (5-HT) function is associated

with NSSI, impaired emotion regulation and impulsivity. We investigated the effects of

experimentally lowered 5-HT activity, via acute tryptophan depletion (ATD), on impulsive

action, reflection impulsivity and mood in female adolescents engaging in NSSI. Method.

Thirty-two female adolescents engaging in NSSI participated in a randomized, double-blind,

parallel group ATD study. Following ATD, impulsive action was assessed using the

Continuous Performance Test, Identical Pairs Version and reflection impulsivity was assessed

using the Matching Familiar Figures Test. Mood-lowering was examined using the Profile of

Mood States. Results. Following ATD, the participants adopted an impulsive response style.

52

ATD did not affect reflection impulsivity or mood. Conclusions. In addition to causing an

impulsive response style, ATD caused increased attentional capacity. Thus, the impulsive

response style was characterized as being focused and directed, as one of functional

impulsivity resulting in an optimal test performance. The findings might suggest that low

serotonin function triggers this particular group of female adolescents to impulsively engage

in NSSI when in emotional distress.

53

Discussion

The overall aim of the present study was to gain more knowledge on some potentially

relevant factors concerning the reasons why adolescents engage in NSSI. Within this wide,

far-reaching context, we investigated various aspects of neuropsychological functions in

adolescents engaging in NSSI, as well as the effects of low serotonin function, via acute

tryptophan depletion, on impulsivity and mood in female adolescents engaging in NSSI. The

study was well-designed to address the specific research aims. Still, a critical examination and

discussion of the findings are needed to yield some indications as to what the findings actually

might mean. In addition, some methodological issues need to be addressed. Nevertheless, the

present findings might help illuminate some aspects of the neuropsychological and

serotonergic functioning that might be involved in NSSI. Thus, in essence the present research

findings contribute to the puzzle of understanding why adolescents engage in NSSI.

Discussion of Main Findings

As reported in paper I, with respect to the investigation of the three main aspects of

executive functions, i.e., shifting, updating and inhibition (Miyake et al., 2000), we found that

the high-severity NSSI group had working memory deficits, while the low-severity NSSI

group had impaired inhibitory control. Neither NSSI subgroups had shifting deficits. No

significant group differences in IQ strengthen the conclusion that the results reflect

impairments in specific aspects of executive functions and not group differences in general

cognitive abilities. Furthermore, those meeting criteria for a current or a previous MDD did

not perform worse on the executive function tests than those who did not meet the criteria.

This indicates that the impairments in executive functions in adolescents engaging in NSSI is

not just an expression of an underlying psychological disorder. The working memory deficits

54

were most pronounced in males in the high-severity NSSI group, however, the same pattern

was evident in their female counterparts.

These findings suggest that the NSSI subgroups have selective deficits in executive

functions, thereby yielding knowledge regarding specific aspects of neuropsychological

functioning that might be involved in NSSI in adolescents. Both working memory and

inhibition are related to emotion regulation (Nash et al., 2007; Schmeichel et al., 2008; Van

Dillen & Koole, 2007). Consequently, the findings of selective deficits in these aspects of

executive functions might suggest that the ability to regulate emotions per se is impaired in

adolescents engaging in NSSI, thereby indirectly suggesting that they struggle with regulating

their emotions. Along these lines, the present neuropsychological findings corroborate and

extend previous findings showing that adolescents typically report that they engage in NSSI to

regulate their emotions (Kumar et al., 2004; Laye-Gindhu & Schonert-Reichl, 2005; Nock &

Prinstein, 2004; Penn et al., 2003; Ross & Heath, 2003). In sum, the present findings might

indirectly support the emotion regulation hypothesis of NSSI from a neuropsychological

perspective.

As reported in paper II, the systematic investigation of the various subcomponents of

verbal learning and memory revealed that adolescents engaging in NSSI had impaired

immediate memory span and verbal learning. In addition, males in the NSSI group had

deficits in immediate and delayed recall and in recognition. However, they remembered most

of what they learned, suggesting that their primary difficulties reside in a reduced amount of

learning or encoded information to begin with, rather than additional impairments in recall

and recognition as such. No group differences were found on the intrusion or the interference

measure. Again, no group differences in IQ strengthen the conclusion that the results reflect

55

deficits in specific aspects of verbal learning and memory and not between-group differences

in intellectual functioning.

The finding of impaired immediate memory span extends the findings reported in

paper I of impaired spatial working memory in adolescents engaging in NSSI, suggesting

impaired short-term memory and working memory irrespective of modality in this specific

group of adolescents. Importantly, tasks that primarily are short-term memory tasks for some

individuals are working memory tasks for others because individuals differ in reliance on the

central executive in performing the tasks (Engle, Tuholski, Laughlin, & Conway, 1999).

Furthermore, the finding of impaired verbal learning suggests difficulty in long-term memory

encoding abilities (Talley, 1993). However, MDD also had a significant effect on the

particular measure reflecting long-term memory encoding abilities. Still, the effect of NSSI on

this measure remained nearly significant, whereas the effect of current MDD disappeared,

when included in the same analysis. Thus, although only at trend-level, NSSI continued to

have an effect on verbal learning when controlling for MDD.

Besides the results regarding long-term memory encoding abilities, the findings

suggest that deficits in specific aspects of verbal learning and memory are associated with

NSSI independently of psychiatric diagnoses. Importantly, the findings might be relevant in

applied settings as scores on verbal learning and memory tests are associated with academic

achievements (Talley, 1993). As we did not include a measure of academic attainments, we

cannot know whether performance on verbal learning and memory tests predict scholastic

achievements in this particular adolescent group. Nevertheless, the present findings might be

seen as a first reasonable step in investigating whether adolescents engaging in NSSI may

need training to improve their verbal learning and memory, which in turn might affect their

academic attainments.

56

In addition, the findings contribute further to the comprehension of some aspects of

neuropsychological functioning that might be involved in NSSI. Impaired short-term

memory/working memory might be one underlying problem in adolescents engaging in NSSI,

as these impairments might indirectly contribute to their difficulty in regulating emotions, as

discussed above. Furthermore, the struggling with regulating emotions in these adolescents

might in turn consume their cognitive resources that are necessary for verbal encoding of

memories, thereby possibly in a viscous circle, further aggravating their impaired learning and

short-term memory/working memory (Richards & Gross, 2000). At a neurobiological level,

this constellation of findings suggests an inefficient network comprising frontal cortex

structures and more posterior cortical structures being involved in NSSI.

As reported in paper III, the main finding in the experimental session of the study was

that ATD caused increased impulsive action in female adolescents engaging in NSSI.

However, ATD did not affect reflection impulsivity or mood in the female adolescents.

Unexpectedly, ATD also caused increased discriminability and attention. Thus, their

impulsive response style following ATD appeared focused and directed. This contrasts with

the prevailing conceptualization of impulsive behaviours, as engaged in impetuously, lacking

deliberation and regard for the consequences (Cherkasky & Hollander, 1997). In sum, as the

response style adopted by the tryptophan-depleted female adolescents resulted in an optimal

test performance, it can perhaps be best described as one of functional impulsivity (Dickman,

1990). Intriguingly, our findings corroborate previous findings of this specific type of

impulsive response style following ATD with remitted depressed patients with a history of

suicidal ideation (Booij et al., 2006), suggesting that low 5-HT function leads to a specific

type of focused and directed impulsive response style in these quite similar groups struggling

with self-injury. Furthermore, ATD had no effects on reflection impulsivity in female

57

adolescents engaging in NSSI, suggesting that low 5-HT function and impulsive action are

specifically involved in NSSI. The findings of increased impulsive action and no mood-

lowering following ATD might suggest that female adolescents engaging in NSSI have a

reflexive tendency toward impulsive action, as opposed to a reflexive tendency toward

freezing, avoidance and inaction, associated with depression vulnerability (Carver, Johnson,

& Joormann, 2008). In sum, the ATD findings might suggest that low serotonin is involved in

impulsive action in this adolescent group, and further that this specific type of impulsive

action might be triggered in the face of psychological distress. Specifically, the findings might

imply that low serotonin function triggers this particular group of female adolescents to

impulsively engage in NSSI when in emotional distress. As adolescents typically report that

their negative emotions are reduced during and after self-injuring (Laye-Gindhu & Schonert-

Reichl, 2005; Ross & Heath, 2003), the present finding of impulsive action following ATD

might possibly be relevant for emotion regulation in female adolescents engaging in NSSI.

Summing up, the main findings of the study advance the understanding of specific

aspects of neuropsychological functioning that might be involved in NSSI in adolescents.

Impaired executive functions seem to be particularly involved in NSSI. Also, the findings

contribute to elucidate the role of low serotonin function and impaired impulse control that

might be involved in NSSI. However, some of the findings are in need of even further

examination and discussion.

Findings with respect to impulsivity across NSSI subgroups and sessions. The

Stop Signal Task (SST; Logan et al., 1984) and the Continuous Performance Test, Identical

Pairs Version (CPT-IP; Cornblatt et al., 1988) used in the respective test and experimental

sessions of the study, both measure impulsive action or the ability to inhibit a dominant motor

response (Robbins & Crockett, 2010). As reported and discussed in paper I, only the low-

58

severity NSSI group showed inhibition deficits, as measured by the SST. Thus, the high-

severity NSSI group did not show impaired performance on the SST. However, when

tryptophan-depleted (paper III), the adolescent females engaging in NSSI adopted an

impulsive response style, as shown by their low β-value on the CPT-IP. An equal number of

adolescent females in the low-and high-severity NSSI subgroups participated in the ATD

session. Hence, although only one NSSI subgroup showed impulsivity in the ordinary

neuropsychological test session (paper I), ATD triggered impulsivity in general in female

adolescents engaging in NSSI (paper III).

Although the CPT-IP and the SST both measure the response inhibition aspect of

impulsivity (Robbins & Crockett, 2010), there might be subtle differences in which aspects of

response inhibition they measure (Robbins & Crockett, 2010). Presuming that the CPT-IP

requires Go/NoGo discrimination, in the CPT-IP, inhibition has to be exerted in the response

selection phase (Robbins & Crockett, 2010). On the contrary, in the SST, response selection

has already occurred but the performance of the response has to be curtailed (Robbins &

Crockett, 2010). Thus, our findings might suggest that the adolescents in the low-severity

NSSI group struggle with behavioural disinhibition both before (CPT-IP) as well as after

response selection (SST). Along these lines, our findings might further suggest that the

impaired impulse control in the adolescents in the high-severity NSSI group only involves

behavioural disinhibition before (but not after) response selection. Thus, the use of different

tests measuring subtly different aspects of response inhibition might have captured distinct

deficits in response inhibition in the two NSSI subgroups. However, in addition to the use of

different response inhibition tests, the sessions of the study in which they were performed in,

involved completely different conditions. We did not employ identical tests of response

inhibition in the two sessions of the study. Accordingly, we can not disentangle whether the

59

inconsistent findings with respect to response inhibition in the high-severity NSSI group

across study sessions, were due to the use of different tests or the different conditions in

which they were performed. To be able to disentangle these different possibilities, we should

have used exactly the same test of response inhibition in both sessions of the study.

Indeed, as described in paper I and paper III, the contexts in which the tests of

response inhibition were completed, were to a high degree dissimilar. When completing the

SST (paper I), the adolescents met at the Department of Psychology for undergoing a

straightforward neuropsychological testing session. This represented a more or less neutral

test situation, at least in the sense that we did not experimentally induce stress as the context

for the testing session. In contrast, when completing the CPT-IP (paper III), the adolescents

were exposed to ATD. Decreased serotonin neurotransmission, induced by ATD, might be

understood as stress, even though it contrasts with the traditional focus on environmental

stress. A main advantage of this biological operationalization of stress, is that the serotonin

system is challenged directly, thereby eliminating individual differences in subjective

perception and reporting of stress. As stress is experimentally induced, it is more controlled

than naturally occurring negative life events, used as operationalizations of stress in previous

studies (Dykman & Johll, 1998; Hankin, Abramson, Miller, & Haeffel, 2004). Adolescents

engaging in NSSI typically report strong negative emotional states as leading up to self-

injuring (Laye-Gindhu & Schonert-Reichl, 2005; Ross & Heath, 2003), suggesting that they

might impulsively engage in NSSI only when under extreme stress or in psychological

distress (Janis & Nock, 2009). Thus, the stressful context in which the CPT-IP was

completed, might be analogous to the emotional distress that often is reported as leading up to

self-injuring.

60

Hence, the findings reported in paper I and paper III might suggest that stress is

needed to elicit an impulsive response style in adolescents in the high-severity NSSI group.

This comprehension is compatible with two-mode models of self-regulation (Carver et al.,

2008). Specifically, serotonin function is important for executive control processes that inhibit

behaviour patterns influenced by the reflexive or reactive system (Carver et al., 2008). By

temporarily decreasing 5-HT neurotransmission by ATD, the finding of increased impulsive

action (paper III) suggests that female adolescents engaging in NSSI have a reflexive

tendency toward impulsive action (Carver et al., 2008). Importantly, the reflexive system

dominates when a situation is emotionally charged (Carver et al., 2008). Thus, stress either

conceptualized as emotional distress or as experimentally induced lowered serotonin function,

seems necessary to elicit or trigger an impulsive response style in adolescents in the high-

severity NSSI group. This possibility is supported by no findings of increased impulsivity in

this particular NSSI group in the ordinary test session as reported in paper I. Also, the

impulsive response style elicited by ATD was focused and directed. Thus, it could perhaps be

best described as one of functional impulsivity, as it resulted in a beneficial test performance

on the CPT-IP. This specific directed impulsive response style elicited by ATD might be

analogous to the impulsive response stye elicited in the face of emotional distress in real life

in female adolescents engaging in NSSI. Accordingly, the functional impulsive response style

found on the CPT-IP might indicate that this specific type of impulsive response style might

be adaptive in regulating overwhelming emotions in the short run in these adolescents.

Indeed, adolescents find engaging in NSSI as effective at releasing negative affect (Jacobsen

& Gould, 2007). Nevertheless, engaging in NSSI likely have devastating effects in the long

run, worsening symptoms and distress (Jacobsen & Gould, 2007) and precluding engaging in

more abstract and verbal emotion regulation strategies (Ross et al., 2009). Interpreting the

inconsistent findings on impulsivity in the high-severity NSSI group, as suggesting that stress

61

is necessary to trigger a specific impulsive response style in this particular adolescent group,

is in accordance with vulnerability-stress models, stating that both a vulnerability and stress

are needed for a mental disorder to develop (Monroe & Simons, 1991). Thus, the apparently

inconsistent findings in the high-severity NSSI group discussed in paper I and paper III can be

reconciled within such an understanding.

ATD triggered impulsivity in general in adolescents engaging in NSSI. However,

stress was not necessary to elicit impaired response inhibition in the adolescents in the low-

severity NSSI group (paper I). The findings of impaired response inhibition regardless of

stress in the low-severity NSSI group might suggest that these adolescents differ in some

respects from the adolescents in the high-severity NSSI group. There are individual

differences in the degree to which adolescents engage in emotion-based rash action and risky

behaviour (Cyders & Smith, 2008). The impaired response inhibition regardless of stress

found in the adolescents in the low-severity NSSI group might suggest that they are on the

one extreme on this disposition. Within such an understanding, their self-injuring might

primarily reflect impulsive experimenting with these behaviours, rather than impulsively

engaged in when in psychological distress primarily for affect-regulating purposes, which

might seem to be the case for the high–severity NSSI group. Thus, reflecting their inclination

towards engaging in impulsive, risky behaviours, the NSSI behaviours engaged in by the low-

severity NSSI group might primarily reflect benign, clinically insignificant experimenting

with these behaviours. This in contrast to the self-injuring nature of the same behaviours,

reflecting pathological, clinically significant NSSI among the adolescents in the high-severity

NSSI group.

The use of different NSSI subgroups. The investigation of executive functions in

adolescents engaging in NSSI (paper I) was based on a neurobiological model of emotion

62

processing, recognizing the role of executive functions in regulating emotions (Phillips et al.,

2003). In turn, our understanding of executive functions was based on the empirically

supported model of executive functions as consisting of three main aspects, i.e., inhibition,

updating and shifting (Miyake et al., 2000). The exploration of these aspects of executive

functions in the adolescents engaging in NSSI was primarily theoretically driven. Specifically,

it was aimed at increasing the knowledge of specific aspects of executive functioning that

could further help illuminate why adolescents typically report that they engage in NSSI to

regulate emotions (Kumar et al., 2004; Laye-Gindhu & Schonert-Reichl, 2005; Nock &

Prinstein, 2004; Penn et al., 2003; Ross & Heath, 2003). However, NSSI is a heterogeneous

phenomeneon (Lloyd-Richardson et al., 2007; Skegg, 2005; Whitlock et al., 2008). Thus,

from a theoretical stance, it could be that different subgroups of adolescents engaging in NSSI

have distinct deficits in different aspects of executive functions. Thus, to capture such

possible differences between NSSI subgroups, we took the NSSI heterogeneity into

consideration in our theoretically driven investigation of executive functions. Specifically, we

classified the adolescents engaging in NSSI into a low- and a high-severity NSSI subgroup,

respectively, when investigating executive functions in adolescents engaging in NSSI (paper

I).

In contrast to the primarily theoretical stance from which the investigation of exeutive

functions was performed (paper I), the investigation of the various aspects of verbal learning

and memory (paper II), was at least initially driven by a more applied perspective. In essence,

the typical age of onset of NSSI is between 12 and 14 years (Muehlenkamp & Gutierrez,

2007; Nock & Prinstein, 2004; Ross & Heath, 2002). This coincides with adolescence, an

important period for the development of long-term patterns of academic functioning (Lerner,

Ostrom, & Freel, 1997). In children and adolescents, previous studies have shown that various

63

aspects of verbal learning and memory are associated with academic attainments (Kinsella et

al., 1995, 1997; Sujansky, Griffith, & Lefevre, 1996; Talley, 1993). Accordingly, one of the

main aims of the investigation of verbal learning and memory in adolescents engaging in

NSSI was to gain knowledge that could be relevant in applied settings. Specifically, the

investigation could help illuminate whether adolescents engaging in NSSI need training to

improve their verbal learning and memory, which might affect their academic attainments.

Within this applied perspective, we aimed at investigating the level of functioning on verbal

learning and memory as such in adolescents engaging in NSSI, independently of the severity

of their NSSI. Thus, when investigating the various aspects of verbal learning and memory

(paper II), we did not classify the adolescents engaging in NSSI into further subgroups

reflecting low versus high NSSI severity. Instead we treated all adolescents engaging in NSSI

as one NSSI group.

In the experimental session of the study (paper III), we primarily aimed at gaining

knowledge about potential mechanisms as regards to serotonin function, impulsivity and

mood that might be involved in NSSI. To achieve this goal, 42 of 48 of our overall sample of

female adolescents engaging in NSSI, was convenience sampled to participate in the

experiment. We decided not to include all female adolescents engaging in NSSI into the

experiment for several reasons. First, based on previous ATD-studies (Menkes, Coates, &

Fawcett, 1994; Weltzin, Fernstrom, McConaha, & Kaye, 1994) group sizes of approximately

15 adolescents would enable us to detect behavioural and mood effects of ATD. Thus, it was

not necessary to include all the female adolescents in the experiment to investigate our

research aims. Second, there are some potential uncomfortable aspects inherent in

participating in an ATD-study, such as having to fast and ingest an unpalatable amino acid

mixture. Hence, from an ethical perspective, it could hardly be justified to let more

adolescents than strictly necessary to investigate our research aims, undergo the ATD-

64

procedure. In addition, for practical reasons, we decided to use a convenience sample of the

female adolescents engaging in NSSI for participation in the experiment.

The influence of sex on the neuropsychological findings in adolescents engaging

in NSSI. Some previous studies have found significant sex differences in executive functions

(Anderson et al., 2001; Fields et al., 2009; Kalkut et al., 2009) and in verbal learning and

memory (Kramer, Delis, Kaplan, O’Donnell, & Prifitera, 1997) in adolescents. Accordingly,

we decided to investigate the interactive effect of sex when investigating these

neuropsychological functions in adolescents engaging in NSSI. Overall, we found the same

pattern of deficits in specific aspects of the investigated neurospychological functions in male

and female adolescents engaging in NSSI. However, the results revealed some interactions

between group and sex. Specifically, although the adolescents in the high-severity NSSI

group in general showed impaired spatial working memory, the males in this group was

somewhat particularly impaired in this respect. Also, the findings of deficits on measures of

immediate memory span and level of learning, suggested a core problem involving impaired

short-term memory/working memory and difficulty in the encoding of material into long-term

memory in adolescents engaging in NSSI in general. However, as the females engaging in

NSSI showed intact recall and recognition, they seemed to being able to compensate for these

deficits. On the other hand, the males engaging in NSSI were not able to compensate for these

deficits, as they also showed impaired recall and recognition.

Our findings revealing the presence of some interaction effects between different

adolescent groups and sex in neuropsychological functions emphasize the importance of

considering the interactive effect of sex when investigating neuropsychological functions in

various groups in general and perhaps in adolescent groups in particular. Indeed, some

research findings show different developmental trajectories for some neuropsychological

functions in male and female adolescents (Kalkut et al., 2009). By investigating the

65

interactive effect of sex when possible, one might prevent overlooking sex differences that are

specific for some groups. Importantly, such sex differences might be of relevance both with

respect to the understanding of the phenomena of interest as well as to the development of

adequate clinical interventions.

Methodological Considerations

Reliability of findings. The adolescents engaging in NSSI in the present study are

probably not representative of the population of adolescents engaging in NSSI in the

community of Oslo and nearby areas. The same issue of representativity applies to the healthy

adolescent controls. Our sample, both with respect to the adolescents engaging in NSSI and

the healthy control adolescents were not selected randomly from the respective populations of

adolescents engaging in NSSI and adolescents who have never engaged in any NSSI. Instead,

they chose to participate in response to a request, possibly reflecting a particular interest in

participating in a study focusing on neuropsychological functioning. In addition, all

adolescents participating in the present study attended school. Importantly, research findings

show that children and adolescents who do not attend school have higher rates of

psychopathology as compared with children and adolescents without attendance problems

(Egger, Costello, & Angold, 2003). Thus, it is possible that our participants had a higher level

of functioning and education as compared to the average community populations of

adolescents who engage in NSSI and of adolescents who have never engaged in any NSSI,

resepectively. This potential bias might have influenced the present research findings.

Also, the female adolescents engaging in NSSI that underwent the experimental

session of the study, were convenience sampled from our pool of female adolescents engaging

in NSSI. Again, this raises the question of the representativity of this sample of female

adolescent group, and in turn the reliability of the findings from the experimental session. The

66

female adolescents were not randomly selected from either the population of female

adolescents engaging in NSSI nor from the sample of female adolescents engaging in NSSI

who participated in the present study. Again, this potential bias might have influenced the

present research findings.

Furthermore, the relatively few males in our sample raise the question of the reliability

of our findings with respect to deficits in specific aspects of executive functions and in

specific aspects of verbal learning and memory in male adolescents engaging in NSSI. By

interpreting our findings as reflecting real group differences, there is a risk of committing a

type I error. However, rejecting our findings entails the possibility of committing a type II

error. The risk of committing a type I error seems justified considering the potential negative

consequences of ignoring our findings of specific neuropsycological impairments in male

adolescents engaging in NSSI. However, the reliability of our findings with male adolescents

engaging in NSSI will be strengthened if replicated with samples including more males.

External validity of findings. The participants in the present study were recruited

exclusively from high schools. Thus, all participants, including the adolescents engaging in

NSSI, were community sampled. Throughout all sessions of the study, the vast majority of the

adolescents engaging in NSSI attended school and appeared to be functioning adequately.

Thus, our community sample might differ from samples recruited exclusively from clinics,

outpatient or inpatient units which often indicate a significant loss of functioning across a

wide range of areas in their lives. Hence, one cannot know whether the present findings

regarding adolescents engaging in NSSI can be generalized to clinical populations of

adolescents struggling with NSSI.

However, as reported in paper I, the present findings show that the community

sampled adolescents engaging in NSSI had elevated levels of symptoms of depression and

67

anxiety as well as of experienced and expressed anger. A considerable number of them met

criteria for at least one psychiatric diagnosis, especially MDD. Although not identical and

surely not of the same degree of severity, the present pattern of associated psychiatric

symptoms and diagnoses in the adolescents engaging in NSSI resemble what is found in

clinical samples of adolescents engaging in NSSI (Jacobsen et al., 2008; Nock et al., 2006). In

addition, a substantial number of the community sampled adolescents engaging in NSSI had

received or still received help from the school health services or the local mental health

services. In sum, in certain respects the adolescents performing NSSI in the present study

resembled clinical populations of adolescents engaging in NSSI. Nevertheless, as they were

recruited exclusively from schools, they might differ from clinical populations of adolescents

engaging in NSSI, in important ways that might have influenced the present findings.

Also, closely related, one might question whether the NSSI engaged in by the

community sampled adolescents is the same phenomena of NSSI engaged in by clinical

populations of adolescents. Indeed, the behaviours that qualify for NSSI and those that are of

clinical significance are unresolved issues (Lloyd-Richardson et al., 2007). Still, as the

questionnaire that we used to screen for NSSI has been used to capture NSSI in clinical

samples of adolescents (Guertin et al., 2001; Nock & Prinstein, 2004), the NSSI phenomena,

at least at a behavioural or phenomenological level, seems similar across samples. In addition,

our decision to use as criteria for inclusion in the NSSI group that the adolescents had

engaged in at least two different NSSI behaviours during the past year, was chosen to exclude

adolescents only endorsing the item “picked at a wound,” as it in isolation may reflect non-

pathological, non–NSSI (Lloyd-Richardson et al., 2007). Furthermore, research findings show

that the same biochemical dysfunction might underlie self-injurious behaviours that vary in

68

severity and aggression (Stanley et al., 1992), suggesting that the present findings might be

generalizable to NSSI of varying severity.

Still, it seems reasonable to assume that the NSSI engaged in by the community

adolescents in the present study might not be as severe as the NSSI engaged in by clinical

populations of adolescents. Accordingly, the use of a community sample might seem to

involve a particular conservative test when investigating specific aspects of

neuropsychological functioning that might be involved in NSSI. Also, it seems reasonable to

assume that the psychological problems reported by the community sampled adolescents

engaging in NSSI, at least at a group level, were less severe as compared with psychological

problems from which clinical adolescent populations suffer. Supporting this assumption,

although a considerable number of the community sampled adolescents engaging in NSSI

suffered from psychological problems, the vast majority of them attended school and

appeared to function adequately in their lives throughout all sessions of the study. Thus, there

are reasons to believe that the present findings with a community sample at least to a lesser

extent are contaminated by impairments associated with clinical samples. This suggests that

the present findings might give a clearer picture of the neuropsychological functions that

might be involved in NSSI.

Nevertheless, studying such a community sample, which thus to a lesser extent is

confounded by comorbid problems that might influence the results in a clinical sample, raises

the question of the generalizability of the results to clinical populations. Ultimately, it is an

empirical question whether the present findings are generalizable to adolescent clinical

populations engaging in NSSI as well as to clinical populations engaging in NSSI at other age

groups than adolescence.

69

Clinical Implications

The present findings involve statistically significant differences between groups on

some behavioural measures of neuropsychological functioning. However, statistically

significant group differences do not necessarily translate to clinically significant group

differences. Thus, even though the findings show statistically significant differences between

groups on specific aspects of neuropsychological functions, it remains an empirical question

to find out whether the statistically significant group differences are of clinical relevance. This

should be kept in mind when considering potential clinical implications of the present

findings. Also, one has to be aware of the fact that the research findings are at a group level.

Thus, one cannot know whether the findings and their ensuing clinical implications are

relevant for each and every adolescent engaging in NSSI. However, the findings at the group

level nevertheless show the importance of completing a neuropsychological and a clinical

assessment when encountering the individual adolescent engaging in NSSI in a clinical

setting. Indeed, the clinical implications primarily pertain to the neuropsychological and

clinical assessment of adolescents engaging in NSSI.

First, as reflected in the findings, a neurospsychological assessment might yield

important clinical information. Such an assessment might uncover selective deficits in

specific aspects of executive functions as well as in aspects of verbal learning and memory

that might be of clinical utility. Specifically, if such deficits are found in the individual

adolescent struggling with NSSI, they should be taken in consideration when planning

therapeutic interventions. Indeed, the present findings showing that NSSI subgroups have

distinct deficits in executive functions suggest that engaging in NSSI might have different

functions for different adolescents. This further emphasizes that performing a

neuropsychological assessment in a clinical setting might yield clinical information that is

70

valuable to meet the specific therapeutic needs of the individual adolescent engaging in NSSI.

The finding of no deficits with respect to general cognitive functioning further emphazises the

importance of performing a neuropsychological assessment with this adolescent group.

Normal general cognitive functioning might make it difficult to notice deficits in specific

aspects of neuropsychological funtioning, which might be revealed first through a thorough

neuropsychological assessment.

Second, a clinical assessment in general and a diagnostic evaluation in particular

should be performed with adolescents engaging in NSSI. As reported in paper I, the research

findings show that NSSI is associated with symptoms of depression and anxiety as well as

heightened levels of both experienced and expressed anger. With respect to psychiatric

diagnoses (also reported in paper I) NSSI is particularly associated with MDD, and also there

was a tendency for an association with social phobia. Thus, in light of the associations

between NSSI and these clinical symptoms and diagnoses, a diagnostic assessment of

adolescents engaging in NSSI seems to be of clinical value. As with a neuropsychological

assessment, a diagnostic assessment can provide clinical information that is needed to tailor

the therapeutic needs to each adolescent struggling with NSSI.

The present research findings also have clinical implications that might be relevant for

the treatment of NSSI in adolescents. Research clearly is needed to establish these clinical

implications, so for now they can only be considered as preliminary implications. First, as

selective deficits in specific aspects of executive functions as well as in specific aspects of

verbal learning and memory can represent neuropsychological mechanisms that might be

involved in NSSI, training programmes specifically aimed at improving these impaired

functions might possibly improve these specific functions and thereby possibly reduce NSSI.

At the moment, this possibility certainly only can have the status as a potential implication of

71

our findings. Still, this possible clinical implication is in accordance with research showing

beneficial effects of training working memory on other aspects of executive functions and on

ADHD symptoms in children (Klingberg et al., 2005).

Second, the present findings indicate that the impulsive response style in adolescents

engaging in NSSI primarily is triggered by stress as when in psychological distress. This

might imply that the identification and recognition of factors that elicit psychological distress

could be an important therapeutic focus to reduce the occurrence of impulsively engaging in

NSSI when in psychological distress. Also, this might imply that the development of more

adaptive strategies both for managing stressful situations and for regulating emotions, given

that NSSI is engaged in for affect-regulating purposes, should be targeted in therapy.

Third, the finding of low serotonin being involved in the impulsive response style

might suggest that the administration of SSRIs might help reduce NSSI in adolescents. This is

consistent with research findings showing that SSRIs reduced non-suicidal self harm in

adolescents with depression (Goodyer et al., 2007).

Future Perspectives

The present study primarily investigated the reasons why adolescents engage in NSSI

within a neuropsychological/biological framework. Further research with other perspectives

are needed to reach the overall aim of gaining more knowledge on the reasons why

adolescents engage in NSSI.

Since reseach findings suggest a role for executive functions in emotion regulation

(Phillips et al., 2003; Schmeichel et al., 2008; Van Dillen & Koole, 2007), the present

findings of impaired executive functions in adolescents engaging in NSSI, might suggest that

this adolescent group struggles with regulating emotions. However, as we did not include any

72

direct measure of emotion dysregulation, the present findings only indirectly can support the

emotion regulation hypothesis from a neuropsychological perspective. Nevertheless, in this

research project we wanted to test specific executive functions found to be involved in the

ability to regulate emotions per se. Thus, our investigation of executive functions in this

adolescent group was a first reasonable step in increasing knowledge on the emotion

regulation hypothesis of NSSI (Jacobsen & Gould, 2007) from a neuropsychological

perspective. Surely, future studies further investigating the emotion regulation hypohesis,

should include direct measures of emotion dysregulation. Relatedly, future studies are needed

to investigate whether this adolescent group also have increased emotional reactivity, which

constitutes another important vulnerability for emotional dysregulation (Nock, Wedig,

Holmberg, & Hooley, 2008). In close association with this, a recent study found that

adolescents engaging in NSSI showed higher physiological reactivity, as measured by skin

conductance, during a distressing task as compared with healthy controls (Nock & Mendes,

2008). Still, including specific measures of emotional reactivity in future research are

essential to investigate whether adolescents engaging in NSSI also have a vulnerability in this

respect, and thus to explore the emotion regulation hypothesis of NSSI even further.

Considering the heterogeneous nature of NSSI (Lloyd-Richardson et al., 2007; Skegg,

2005; Whitlock et al., 2008), we classified the adolescents engaging in NSSI into two NSSI

subgroups reflecting low and high severity NSSI, when investigating the aspects of executive

functions (paper I). Our procedure for classification was based on a thorough literature

review, showing that the the NSSI forms and the number of different NSSI behaviours

engaged in are particularly important in distinguishing NSSI severity (Jacobsen & Gould,

2007; Whitlock et al., 2008). However, future studies are needed to further investigate the

validity of the NSSI subgroups resulting from this particular classification procedure.

73

Specifically, such studies should be undertaken to investigate the discriminative validity of

these NSSI subgroups, i.e., whether the NSSI subgroups differ in further respects that makes

sense theoretically and clinically. The findings from such studies, investigating the

discriminative validity of the NSSI subgroups, will in turn either support or discourage further

use of this particular classification procedure. Furthermore, considering the heterogeneous

nature of NSSI, it would be interesting to explore individual differences within the overall

NSSI group in future studies.

A longitudinal study following community sampled preadolescents that never have

engaged in any NSSI into adolescence would be of great interest. Such a longitudinal study

could involve neuropscyhological testing, clinical evaluations and screening of NSSI at

several time points, and thereby help illuminate the chronological associations between

deficits in specific aspects of neuropsychological functions, symptoms of psychological

disorders as well as onset of engaging in NSSI. Thus, a longitudinal study could help

answering whether the deficits in specific aspects of neuropsychological functions are present

before onset of engaging in NSSI and thus whether they might represent vulnerabilities for

engaging in NSSI or on contrary are concomitants or consequences of engaging in NSSI.

Future research should also focus on the functional consequences of deficits in specific

aspects of executive functions as well as in verbal learning and memory in adolescents

engaging in NSSI. Considering that adolescence is an important period for the development of

long-term patterns of academic functioning (Lerner et al., 1997), one perhaps particularly

important focus for future studies is to investigate whether specific neuropsychological

deficits are associated with lower academic achievements in adolescents engaging in NSSI.

Thus, future neuropsychological studies that include measures of functional consequences in

general and academic attainments in particular are needed to specify the connection between

74

deficits in specific aspects of neuropsychological functions and their functional consequences

in this specific adolescent group.

Further studies are also wanted to investigate the effects of ATD on dimensions of

impulsivity and mood in healthy adolescent females and males. Findings from such studies

are needed to disentangle whether the present effects of ATD on impulsivity and mood are

merely age- or sex-dependent, or really represent distinctive qualities in adolescent females

engaging in NSSI. Such future studies should also include adolescent males engaging in

NSSI to investigate whether there are sex-specific effects of ATD on dimensions of

impulsivity and mood in adolescents engaging in NSSI in particular. Studies should also

investigate the effects of ATD on impulsivity and mood in adolescents recruited from clinical

populations. This will help clarify whether ATD influences dimensions of impulsivity and

mood in the same vein in a clinical group as in the present community sampled group of

adolescents, thus either supporting or discouraging the external validity of the present

findings.

Considering that there are various subtypes of impulsivity (Evenden, 1999;

Winstanley et al., 2004), future studies are also needed to investigate additional subtypes of

impulsivity in adolescents engaging in NSSI. Performance on behavioural tasks measuring

various forms of impulsivity should be assessd both in ordinary neuropsychological test

sessions as well as in sessions involving experimental manipulations of level of stress.

Findings from such studies might further advance our knowledge both of which specific

forms of impulsivity that might be involved in NSSI and of the specific circumstances in

which they are apparent or elicited.

75

Studies on the treatment of NSSI should investigate neuropsychological functions at

the start of treatment. By doing so, one could investigate both the prognostic value of

neuropsychological variables on the efficacy of various treatments as well as the effects on

neuropsychological functions of the various treatments offered to this specific adolescent

group.

76

Conclusions

One main finding of the present study is that NSSI subgroups have distinctive deficits

in executive functions. The high-severity NSSI group has working memory deficits, while the

low-severity NSSI group has impaired inhibitory control. This indirectly supports the emotion

regulation hypothesis. Another main finding is that adolescents engaging in NSSI exhibit

impairments in verbal learning and memory. The core problems involve impaired short-term

memory/working memory and difficulty in the encoding of material into long-term memory.

This suggests that an inefficient network comprising frontal cortex and more posterior

structures are involved in NSSI. Following ATD, female adolescents engaging in NSSI

adopted a focused and directed impulsive response style. This findings might suggest that low

serotonin function triggers this particular group of female adolescents to impulsively engage

in NSSI when in emotional distress. This might possibly be relevant for emotion regulation in

female adolescents engaging in NSSI.

77

References

Adewuya, A. O., Ola, B. A., & Aloba, O. O. (2007). Prevalence of major depressive disorders

and a validation of the beck depression inventory among nigerian adolescents. European

Child and Adolescent Psychiatry, 16, 287-292. doi: 10.1007/s00787-006-0557-0

Ambrosini, P. J., Metz, C., Bianchi, M. D., Rabinovich, H., & Undie, A. (1991). Concurrent

validity and psychometric properties of the Beck Depression Inventory in outpatient

adolescents. Journal of the American Academy of Child and Adolescent Psychiatry, 30,

51-57.

American Psychiatric Association. (1994). Diagnostic and statistical manual of mental

disorders (fourth edition). Washington, DC: American Psychiatric Association.

American Psychiatric Association. (2010). Proposed revision in the American Psychiatric

Association DSM-5. Retrieved from http://www.dsm5.org/Proposed Revisions/Pages/

proposedrevision.aspx?rid=443

Anderson, V. (1998). Assessing executive functions in children: biological, psychological, and

developmental considerations. Neuropsychological Rehabilitation, 8, 319-349. doi:

10.1080/713755568

Anderson, V. A., Anderson, P., Northam, E., Jacobs, R., & Catroppa, C. (2001). Development

of executive functions through late childhood and adolescence in an Australian sample.

Developmental Neuropsychology, 20, 385-406. doi: 10.1207/S15326942DN2001_5

Barrera, M., & Garrison-Jones, C. V. (1988). Properties of the Beck Depression Inventory as a

screening measure for adolescent depression. Journal of Abnormal Child Psychology,

16, 263-273. doi: 10.1007/BF00913799

78

Bearden , C. E., Hoffman, K. M., & Cannon, T. D. (2001). The neuropsychology and

neuroanatomy of bipolar affective disorder: a critical review. Bipolar Disorders, 3, 106-

150. doi: 10.1034/j.1399-5618.2001.030302.x

Beck, A. T., Epstein, N., Brown, G., & Steer, R. A. (1988). An inventory for measuring clinical

anxiety: Psychometric properties. Journal of Consulting and Clinical Psychology, 56,

893-897. Retrieved from http://www.apa.org/pubs/ journals/ccp/ index.aspx

Beck, A. T., Steer, R. A., & Garbin, M. G. (1988). Psychometric properties of the Beck

depression inventory: Twenty-five years of evaluation. Clinical Psychology Review, 8,

77-100.

Becker, D. F., Grilo, C. M., Edell, W. S., & McGlashan, T. H. (2000). Comorbidity of

borderline personality disorder with other personality disorders in hospitalized

adolescents and adults. The American Journal of Psychiatry, 157, 2011-2016. doi:

10.1176/appi.ajp.157.12.2011

Bell, C. J., Hood, S. D., & Nutt, D. J. (2005). Acute tryptophan depletion. Part II: clinical

effects and implications. Australian and New Zealand Journal of Psychiatry, 39, 565-

574. doi: 10.1111/j.1440-1614.2005.01628.x

Booij, L., Swenne, C. A., Brosschot, J. F., Haffmans, P. M. J., Thayer, J. F., & Van der Does,

A. J. W. (2006). Tryptophan depletion affects heart rate variability and impulsivity in

remitted depressed patients with a history of suicidal ideation. Biological Psychiatry, 60,

507-514. doi:10.1016/j.biopsych.2006.02.010

Borkowska, A., & Rybakowski, J. K. (2001). Neuropsychological frontal lobe testsindicate that

bipolar depressed patients are more impaired than unipolar. Bipolar Disorders, 3, 88-94.

doi: 10.1034/j.1399-5618.2001.030207.x

79

Briere, J., & Gil, E. (1998). Self-mutilation in clinical and general population samples:

prevalence, correlates, and functions. The American Journal of Orthopsychiatry, 68,

609-620. doi: 10.1037/h0080369

Cairns, E., & Cammock, T. (1978). Development of a more reliable version of the Matching

Familiar Figures Test. Developmental Psychology,14, 555-560. doi: 10.1037/0012-

1649.14.5.555

Cambridge Cognition. (2006). CANTABeclipse version 3. Test administration guide.

Cambridge: Cambridge Cognition Limited.

Canli, T., & Lesch, K.- P. (2007). Long story short: the serotonin transporter in emotion

regulation and social cognition. Nature Neuroscience, 10, 1103-1109.

doi:10.1038/nn1964

Carver, C. S., Johnson, S. L., & Joormann, J. (2008). Serotonergic function, two-mode models

of self-regulation, and vulnerability to depression: what depression has in common with

impulsive aggression. Psychological Bulletin, 134, 912-943. doi: 10.1037/a0013740

Chamberlain, S. R., Fineberg, N. A., Blackwell, A. D., Robbins, T. W., & Sahakian, B. J.

(2006). Motor inhibition and cognitive flexibility in obsessive-compulsive disorder and

trichotillomania. The American Journal of Psychiatry, 163, 1282-1284. doi:

10.1176/appi.ajp.163.7.1282

Cherkasky, S., & Hollander, E. (1997). Neuropsychiatric aspects of impulsivity and

aggression. In S. C. Yudofsky, & R. E. Hales (Eds.), The American psychiatric press

textbook of neuropsychiatry, 3rd edn. (pp. 485-499). Washington, DC: American

Psychiatric Press, Inc.

80

Clark, L., Roiser, J. P., Cools, R., Rubinsztein, D. C., Sahakian, B. J., & Robbins, T. W. (2005).

Stop signal response inhibition is not modulated by tryptophan depletion or the

serotonin transporter polymorphism in healthy volunteers: implications for the 5-HT

theory of impulsivity. Psychopharmacology, 182, 570-578. doi: 10.1007/s00213-005-

0104-6

Conners, C. K., Epstein, J. N., Angold, A., & Klaric, J. (2003). Continuous performance test

performance in a normative epidemiological sample. Journal of Abnormal Child

Psychology, 31, 555-562. doi: 10.1023/A:1025457300409

Cornblatt, B. A., & Malhotra, A. K. (2001). Impaired attention as an endophenotype for

molecular genetic studies of schizophrenia. American Journal of Medical Genetics, 105,

11-15. doi:: 10.1002/1096-8628(20010108)105:1<11::AID-AJMG1045>3.0.CO;2-G

Cornblatt, B. A., Risch, N. J., Faris, G., Friedman, D., & Erlenmeyer-Kimling, L. (1988). The

continuous performance test, identical pairs version (CPT-IP): I. new findings about

sustained attention in normal families. Psychiatry Research, 26, 223-238. doi:

10.1016/0165-1781(88)90076-5

Crean, J., Richards, J. B., & de Wit, H. (2002). Effect of tryptophan depletion on impulsive

behavior in men with or without a family history of alcoholism. Behavioural Brain

Research, 136, 349-357. doi: 10.1016/s0166-4328(02)00132-8

Crowell, S. E., Beauchaine, T. P., McCauley, E., Smith, C. J., Vasilev, C. A., & Stevens, A. L.

(2008). Parent-child interactions, peripheral serotonin, and self-inflicted injury in

adolescents. Journal of Consulting and Clinical Psychology, 76, 15-21.

doi:10.1037/0022-006X.76.1.15

81

Cyders, M. A., & Smith, G. T. (2008). Emotion-based dispositions to rash action: positive and

negative urgency. Psychological Bulletin, 134, 807-828. doi: 10.1037/a0013341

Davidson, R. J., Putnam, K. M., & Larson, C. L. (2000). Dysfunction in the neural circuitry of

emotion regulation- a possible prelude to violence. Science, 289, 591-594. doi:

10.1126/science.289.5479.591

De Jong, R., Coles, M. G. H., Logan, G. D., & Gratton, G. (1990). In search of the point of no

return: The control of response processes. Journal of Experimental Psychology: Human

Perception and Performance, 16, 164-182. doi: 10.1037/0096-1523.16.1.164

Delgado, P. L., Charney, D. S., Price, L. H., Aghajanian, G. K., Landis, H., & Heninger, G. R.

(1990). Serotonin function and the mechanism of antidepressant action: Reversal of

antidepressant-induced remission by rapid depletion of plasma tryptophan. Archives of

General Psychiatry, 47, 411-418. doi: 10.1001/archpsyc.1990.01810170011002

De Luca, C. R., Wood, S. J., Anderson, V., Buchanan, J.-A., Proffitt, T. M., Mahony, K., &

Pantelis, C. (2003). Normative data from the Cantab. I: Development of executive

function over the lifespan. Journal of Clinical and Experimental Neuropsychology, 25,

242-254. doi: 10.1076/jcen.25.2.242.13639

Dickman, S. J. (1990). Functional and dysfunctional impulsivity: personality and cognitive

correlates. Journal of Personality and Social Psychology, 58, 95-102. doi:

10.1037/0022-3514.58.1.95

DiClemente, R. J., Ponton, L. E., & Hartley, D. (1991). Prevalence and correlates of cutting

behavior: Risk for HIV transmission. Journal of the American Academy of Child and

Adolescent Psychiatry, 30, 735-739. doi:10.1016/S0890-8567(10)80007-3

82

Dolan, M., Anderson, I. M., & Deakin, J. F. W. (2001). Relationship between 5-HT function

and impulsivity and aggression in male offenders with personality disorders. British

Journal of Psychiatry, 178, 352-359. doi:10.1192/bjp.178.4.352

Dougherty, D. M., Mathias, C. W., Marsh-Richard, D. M., Prevette, K. N., Dawes, M. A.,

Hatzis, E. S., ... Nouvion, S. O. (2009). Impulsivity and clinical symptoms among

adolescents with non-suicidal self-injury with or without attempted suicide. Psychiatry

Research, 169, 22-27. doi:10.1016/j.psychres.2008.06.011

Dykman, B. M., & Johll, M. (1998). Dysfunctional attitudes and vulnerability to depressive

symptoms: A 14-week longitudinal study. Cognitive Therapy and Research, 22, 337-

352. doi: 10.1023/A:1018705112077

Eagle, D. M., Baunez, C., Hutcheson, D. M., Lehmann, O., Shah, A. P., & Robbins, T. W.

(2007). Stop-signal reaction-time task performance: role of prefrontal cortex and

subthalamic nucleus. Cerebral Cortex, 18, 178–188. doi: 10.1093/cercor/bhm044

Egger, H. L., Costello, E. J., & Angold, A. (2003). School refusal and psychiatric disorders: A

community study. Journal of the American Academy of Child and Adolescent

Psychiatry, 42, 797–807. doi: 10.1097/01.CHI.0000046865.56865.79

Engle, R. W., Tuholski, S. W., Laughlin, J. E., & Conway, A. R. A. (1999). Working memory,

short-term memory, and general fluid intelligence: A latent-variable approach. Journal

of Experimental Psychology: General, 128, 309-331. doi: 10.1037/0096-3445.128.3.309

Epstein, J. N., Erkanli, A., Conners, C. K., Klaric, J., Costello, J. E., & Angold, A. (2003).

Relations between continuous performance test performance measures and ADHD

behaviors. Journal of Abnormal Child Psychology, 31, 543-554. doi:

10.1023/A:1025405216339

83

Evenden, J. L. (1999). Varieties of impulsivity. Psychopharmacology, 146, 348-361. doi:

10.1007/pl00005481

Favazza, A. R. (1998). The coming of age of self-mutilation. The Journal of Nervous and

Mental Disease, 186, 259-268. Retrieved from http://journals.lww.com/jonmd/Fulltext

/1998/05000/The__Coming_of_Age_of_Self_Mutilation.1.aspx

Fields, S., Collins, C., Leraas, K., & Reynolds, B. (2009). Dimensions of impulsive behavior in

adolescent smokers and nonsmokers. Experimental and Clinical Psychopharmacology ,

17, 302-311. doi: 10.1037/a0017185

Garrison, C. Z., Addy, C. L., McKeown, R. E., Cuffe, S. P., Jackson, K. L., & Waller, J. L.

(1993). Nonsuicidal physically self-damaging acts in adolescents. Journal of Child and

Family Studies, 2, 339-352. doi: 10.1007/BF01321230

Goodyer, I., Dubicka, B., Wilkinson, P., Kelvin, R., Roberts, C., Byford, S., … Harrington, R.

(2007). Selective serotonin reuptake inhibitors (SSRIs) and routine specialist care with

and without cognitive behaviour therapy in adolescents with major depression:

randomised controlled trial. British Medical Journal, 335, 142. doi:

10.1136/bmj.39224.494340.55

Gould, M. S., Greenberg, T., Velting, D. M., & Shaffer, D. (2003). Youth suicide risk and

preventive interventions: A review of the past 10 years. Journal of the American

Academy of Child and Adolescent Psychiatry, 42(4), 386-405. doi:

10.1097/01.CHI.0000046821.95464.CF

Gratz, K. L., Conrad, S. D., & Roemer, L. (2002). Risk factors for deliberate self-harm among

college students. American Journal of Orthopsychiatry, 72, 128-140. doi: 10.1037/0002-

9432.72.1.128

84

Gross, J. J., & Levenson, R. W. (1997). Hiding feelings: the acute effects of inhibiting negative

and positive emotion. Journal of Abnormal Psychology, 106, 95-103. doi:

10.1037/0021-843X.106.1.95

Guertin, T., Lloyd-Richardson, E., Spirito, A., Donaldson, D., & Boergers, J. (2001). Self-

mutilative behaviour in adolescents who attempt suicide by overdose. Journal of the

American Academy of Child and Adolescent Psychiatry, 40, 1062-1069. Retrieved from

http://linkinghub.elsevier.com/retrieve/pii/S0890856709604482?showall=true

Hankin, B. L., Abramson, L. Y., Miller, N., & Haeffel, G. J. (2004). Cognitive vulnerability-

stress theories of depression: Examining affective specificity in the prediction of

depression versus anxiety in three prospective studies. Cognitive Therapy and Research,

28, 309-345. doi: 10.1023/B:COTR.0000031805.60529.0d

Harvey, P. O., Le Bastard, G., Pochon, J. B., Levy, R., Allilaire, J. P., Dubois, B., & Fossati, P.

(2004). Executive functions and updating of the contents of working memory in

unipolar depression. Journal of Psychiatric Research, 38, 567-576.

doi:10.1016/j.jpsychires.2004.03.003

Hawton, K., Harriss, L., Hall, S., Simkin, S., Bale, E., & Bond, A. (2003). Deliberate self-harm

in Oxford, 1990–2000: a time of change in patient characteristics. Psychological

Medicine, 33, 987-995. doi: 10.1017/S0033291703007943

Hawton, K., Rodham, K., Evans, E., & Weatherall, R. (2002). Deliberate self harm in

adolescents: self report survey in schools in England. British Medical Journal, 325,

1207–1211. doi: 10.1136/bmj.325.7374.1207

85

Hays, J. R., Reas, D. L., & Shaw, J. B. (2002). Concurrent validity of the Wechsler abbreviated

scale of intelligence and the Kaufman brief intelligence test among psychiatric

inpatients. Psychological Reports, 90, 355-359.

Herba, C. M., Tranah, T., Rubia, K., & Yule, W. (2006). Conduct problems in adolescence:

three domains of inhibition and effect of gender. Developmental Neuropsychology, 30,

659-695. doi: 10.1207/s15326942dn3002_2

Herpertz, S., Sass, H., & Favazza, A. (1997). Impulsivity in self-mutilative behavior:

psychometric and biological findings. Journal of Psychiatric Research, 31, 451-465.

doi:10.1016/S0022-3956(97)00004-6

Hilt, L. M., Cha, C. B., & Nolen-Hoeksema, S. (2008). Nonsuicidal self-injury in young

adolescent girls: moderators of the distress-function relationship. Journal of Consulting

and Clinical Psychology, 76, 63-71. doi:: 10.1037/0022-006X.76.1.63

Hintikka, J., Tolmunen, T., Rissanen, M.-L., Honkalampi, K., Kylma, J., & Laukkanen, E.

(2009). Mental disorders in self-cutting adolescents. Journal of Adolescent Health, 44,

464-467. doi:10.1016/j.jadohealth.2008.10.003

Hurry, J. (2000). Deliberate self-harm in children and adolescents. International Review of

Psychiatry, 12, 31-36. Retrieved from http://search.proquest.com/docview/

213378774?accountid=14699

Håseth, K. J. (1996). The Norwegian adaptation of the State-Trait Anger Expression Inventory.

In C. D. Spielberger, I. G. Sarason, J. M. T. Brebner, E. Greenglass, P. Laungani, & A.

M. O’Roark (Eds.), Stress and emotion: Anxiety, anger, and curiosity, 16 (pp. 83-106).

Philadelphia, US: Taylor & Francis.

86

Jablonska, B., Lindberg, L., Lindblad, F., Rasmussen, F., Ostberg, V., & Hjern, A. (2009).

School performance and hospital admissions due to self-inflicted injury: a Swedish

national cohort study. International Journal of Epidemiology, 38, 1334-1341.

doi:10.1093/ije/dyp236

Jacobson, C. M., & Gould, M. (2007). The epidemiology and phenomenology of non-suicidal

self-injurious behavior among adolescents: a critical review of the literature. Archives of

Suicide Research, 11, 129-147. doi: 10.1080/13811110701247602

Jacobson, C. M., Muehlenkamp, J. J., Miller, A. L., & Turner, J. B. (2008). Psychiatric

impairment among adolescents engaging in different types of deliberate self-harm.

Journal of Clinical Child and Adolescent Psychology, 37, 363–375.

doi:10.1080/15374410801955771

Janis, I. B., & Nock, M. K. (2009). Are self-injurers impulsive?: results from two behavioral

laboratory studies. Psychiatry Research, 169, 261-267. doi:

10.1016/j.psychres.2008.06.041

Johnson, M. H., & Magaro, P. A. (1987). Effects of mood and severity on memory processes in

depression and mania. Psychological Bulletin, 101, 28-40. doi: 10.1037/0033-

2909.101.1.28

Jolly, J. B., Aruffo, J. F., Wherry, J. N., & Livingston, R. (1993). The utility of the Beck

Anxiety Inventory with inpatient adolescents. Journal of Anxiety Disorders, 7, 95-106.

doi:10.1016/0887-6185(93)90008-9

Kagan, J., Pearson, L., & Welch, L. (1966). Conceptual impulsivity and inductive reasoning.

Child Development, 37, 583-594. Retrieved from http://www.jstor.org/stable/1126680

87

Kalkut, E. L., Han, S. D., Lansing, A. E., Holdnack, J. A., & Delis, D. C. (2009). Development

of set-shifting ability from late childhood through early adulthood. Archives of Clinical

Neuropsychology, 24, 565-574. doi:10.1093/arclin/acp048

Kaufman, J., Birmaher, B., Brent, D., Rao, U., Flynn, C., Moreci, P., … Ryan, N. (1997).

Schedule for affective disorders and schizophrenia for school- age children- present and

lifetime version (K-SADS-PL): initial reliability and validity data. Journal of the

American Academy of Child and Adolescent Psychiatry, 36, 980-988. doi:

10.1097/00004583-199707000-00021

Kinsella, G., Prior, M., Sawyer, M., Murtagh, D., Eisenmajer, R., Anderson, V., … Klug, G.

(1995). Neuropsychological deficit and academic performance in children and

adolescents following traumatic brain injury. Journal of Pediatric Psychology, 20, 753-

767. doi: 10.1093/jpepsy/20.6.753

Kinsella, G. J., Prior, M., Sawyer, M., Ong, B., Murtagh, D., Eisenmajer, R., … Klug, G.

(1997). Predictors and indicators of academic outcome in children 2 years following

traumatic brain injury. Journal of the International Neuropsychological Society, 3, 608–

616. Retrieved from http://journals.cambridge.org/action/displayAbstract?fromPage

=online&aid=49229

Klingberg, T., Fernell, E., Olesen, P. J., Johnson, M., Gustafsson, P., Dahlström, K., …

Westerberg, H. (2005). Computerized training of working memory in children with

ADHD- a randomized, controlled trial. Journal of the American Academy of Child and

Adolescent psychiatry, 44, 177-186. Retrieved from http://dionysus.psych.wisc.edu/lit/

Articles/KlingbergT2005a.pdf

88

Kramer, J. H., Delis, D. C., Kaplan, E., O’Donnell, L., & Prifitera, A. (1997). Developmental

sex differences in verbal learning. Neuropsychology, 11, 577-584. doi: 10.1037/0894-

4105.11.4.577

Kumar, G., Pepe, D., & Steer, R. A. (2004). Adolescent psychiatric inpatients’ self-reported

reasons for cutting themselves. Journal of Nervous and Mental Disease, 192, 830-836.

doi: 10.1097/01.nmd.0000146737.18053.d2

Kyte, Z. A., Goodyer, I. M., & Sahakian, B. J. (2005). Selected executive skills in adolescents

with recent first episode major depression. Journal of Child Psychology and Psychiatry,

46, 995-1005. doi: 10.1111/j.1469-7610.2004.00400.x

Larsson, B., & Melin, L. (1990). Depressive symptoms in Swedish adolescents. Journal of

Abnormal Child Psychology, 18, 91-103. doi: 10.1007/BF00919458

Laye-Gindhu, A., & Schonert-Reichl, K. (2005). Nonsuicidal self-harm among community

adolescents: understanding the “whats” and “whys” of self-harm. Journal of Youth and

Adolescence, 34, 447-457. doi: 10.1007/s10964-005-7262-z

Lehnert, K. L., Overholser, J. C., & Spirito, A. (1994). Internalized and externalized anger in

adolescent suicide attempters. Journal of Adolescent Research, 9, 105-119. doi:

10.1177/074355489491008

Lerner, R. M., Ostrom, C. W., & Freel, M. A. (1997). Preventing health-compromising

behaviors among youth and promoting their positive development: A developmental

contexual perspective. In J. Schulenberg, J. Maggs, & K. Hurrelmann (Eds.), Health

risks and developmental transitions during adolescence (pp. 498–521). New York:

Cambridge University Press.

89

Lesch, K.- P. (2005). Alcohol dependence and gene x environment interaction in emotion

regulation: is serotonin the link? European Journal of Pharmacology, 526, 113–124.

doi:10.1016/j.ejphar.2005.09.027

Linehan, M. M., Armstrong, H. E., Suarez, A., Allmon, D., & Heard, H. L. (1991). Cognitive-

behavioral treatment of chronically parasuicidal borderline patients. Archives of General

Psychiatry, 48, 1060-1064. Retrieved from http://archpsyc.ama-assn.org/cgi/

reprint/48/12/1060

Linnoila, M., Virkkunen, M., Scheinin, M., Nuutila, A., Rimon, R., & Goodwin, F. K. (1983).

Low cerebrospinal fluid 5-hydroxyindoleacetic acid concentration differentiates

impulsive from nonimpulsive violent behavior. Life Sciences, 33, 2609-2614.

Lloyd-Richardson, E. E., Perrine, N., Dierker, L., & Kelley, M. L. (2007). Characteristics and

functions on non-suicidal self-injury in a community sample of adolescents.

Psychological Medicine, 37, 1183-1192. doi: 10.1017/S003329170700027X

Logan, G. D., & Cowan, W. B. (1984). On the ability to inhibit thought and action: a theory of

an act of control. Psychological Review, 91, 295-327. doi:10.1037/0033-295X.91.3.295

Logan, G. D., Cowan, W. B., & Davis, K. A. (1984). On the ability to inhibit simple and choice

reaction time responses: a model and a method. Journal of Experimental Psychology :

Human Perception and Performance 10, 276–291. doi: 10.1037/0096-1523.10.2.276

Ludolph, P. S., Westen, D., Misle, B., Jackson, A., Wixom, J., & Wiss, F. C. (1990). The

borderline diagnosis in adolescents: Symptoms and developmental history. The

American Journal of Psychiatry, 147, 470−476.

90

Marcotte, D., Alain, M., & Gosselin, M.-J. (1999). Gender differences in adolescent

depression: Gender-typed characteristics or problem-solving skills deficits? Sex Roles,

41, 31-48. doi: 10.1023/A:1018833607815

Markovitz, P. J., Calabrese, J. R., Schulz, S. C., & Meltzer, H. Y. (1991). Fluoxetine in the

treatment of borderline and schizotypal personality disorders. The American Journal of

Psychiatry, 148, 1064-1067.

Mattanah, J. J. F., Becker, D. F., Levy, K. N., Edell, W. S., & McGlashan, T. H. (1995).

Diagnostic stability in adolescents followed up 2 years after hospitalization. The

American Journal of Psychiatry, 152, 889-894.

Matthews, K., Coghill, D., & Rhodes, S. (2008). Neuropsychological functioning in depressed

adolescent girls. Journal of Affective Disorders ,111, 113-118.

doi:10.1016/j.jad.2008.02.003

McCloskey, M. S., Ben-Zeev, D., Lee, R., Berman, M. E., & Coccaro, E. F. (2009a). Acute

tryptophan depletion and self-injurious behavior in aggressive patients and healthy

volunteers. Psychopharmacology, 203, 53-61. doi: 10.1007/s00213-008-1374-6

McCloskey, M. S., New, A. S., Siever, L. J., Goodman, M., Koenigsberg, H. W., Flory, J. D.,

& Coccaro, E. F. (2009b). Evaluation of behavioral impulsivity and aggression tasks as

endophenotypes for borderline personality disorder. Journal of Psychiatric Research,

43, 1036-1048. doi: 10.1016/j.jpsychires.2009.01.002

McNair, D. M., Lorr, M., & Droppleman, L. F. (1971). Profile of Mood States. San Diego,

California: Educational and Industrial Testing Service.

91

Mendelsohn, D., Riedel, W. J., & Sambeth, A. (2009). Effects of acute tryptophan depletion on

memory, attention and executive functions: a systematic review. Neuroscience and

Biobehavioral Reviews, 33, 926-952. doi: 10.1016/j.neubiorev.2009.03.006

Menkes, D. B., Coates, D. C., & Fawcett, J. P. (1994). Acute tryptophan depletion aggravates

premenstrual syndrome. Journal of Affective Disorders, 32, 37-44. doi:10.1016/0165-

0327(94)90059-0

Messer, S. B, & Brodzinsky, D. M. (1981). Three year stability of reflection-impulsivity in

young adolescents. Developmental Psychology, 17, 848-850. doi:10.1037/0012-

1649.17.6.848

Miller, A. L., Muehlenkamp, J. J., & Jacobsen, C. M. (2008). Fact or fiction: Diagnosing

borderline personality disorder in adolescents. Clinical Psychology Review, 28, 969-

981. doi:10.1016/j.cpr.2008.02.004

Miyake, A., Friedman, N. P., Emerson, M. J., Witzki, A. H., Howerter, A., & Wager, T. D.

(2000). The unity and diversity of executive functions and their contributions to

complex “frontal lobe” tasks: a latent variable analysis. Cognitive Psychology, 41, 49-

100. doi: 10.1006/cogp.1999.0734

Monroe, S. M., & Simons, A. D. (1991). Diathesis- stress theories in the context of life stress

research: Implications for the depressive disorders. Psychological Bulletin, 110, 406-

425. doi: 10.1037/0033-2909.110.3.406

Moore, P., Landolt, H.-P., Seifritz, E., Clark, C., Bhatti, T., Kelsoe, J.,…Gillin, J. C. (2000).

Clinical and physiological consequences of rapid tryptophan depletion.

Neuropsychopharmacology, 23(6), 601-622. doi: 10.1016/S0893-133X(00)00161-5

92

Morgan, M. J., Impallomeni, L. C., Pirona, A., & Rogers, R. D. (2005). Elevated impulsivity

and impaired decision-making in abstinent ecstasy (MDMA) users compared to

polydrug and drug-naive controls. Neuropsychopharmacology, 31, 1562-1573.

doi:10.1038/sj.npp.1300953

Muehlenkamp, J. J. (2005). Self-injurious behavior as a separate clinical syndrome. American

Journal of Orthopsychiatry, 75, 324–333. doi: 10.1037/0002-9432.75.2.324

Muehlenkamp, J. J., & Gutierrez, P. M. (2004). An investigation of differences between self-

injurious behavior and suicide attempts in a sample of adolescents. Suicide and Life-

Threatening Behavior, 34, 12-23. doi: 10.1521/suli.34.1.12.27769

Muehlenkamp, J. J., & Gutierrez, P. M. (2007). Risk for suicide attempts among adolescents

who engage in non-suicidal self-injury. Archives of Suicide Research, 11, 69-82.

doi:10.1080/13811110600992902

Muehlenkamp, J. J., Williams, K. L., Gutierrez, P. M., & Claes, L. (2009). Rates of non-

suicidal self-injury in high school students across five years. Archives of Suicide

Research, 13, 317-329. doi: 10.1080/13811110903266368

Nash, S., Henry, J. D., McDonald, S., Martin, I., Brodaty, H., & Peek-O'Leary, M.-A. (2007).

Cognitive disinhibition and socioemotional functioning in Alzheimer's disease. Journal

of the International Neuropsychological Society, 13, 1060-1064. doi:

10.10170S1355617707071184

Nisbett, R. E., & Wilson, T. D. (1977). Telling more than we can know: verbal reports on

mental processes. Psychological Review, 84, 231-259. Retrieved from http://leeds-

faculty.colorado.edu/junggran/7310/Nisbett_1977.pdf

93

Nock, M. K., Joiner, J. T. E., Gordon, K. H., Lloyd-Richardson, E., & Prinstein, M. J. (2006).

Non-suicidal self-injury among adolescents: Diagnostic correlates and relation to

suicide attempts. Psychiatry Research, 144, 65-72. doi:10.1016/j.psychres.2006.05.010

Nock, M. K., & Mendes, W. B. (2008). Physiological arousal, distress tolerance, and social

problem–solving deficits among adolescent self-injurers. Journal of Consulting and

Clinical Psychology, 76, 28-38. doi: 10.1037/0022-006X.76.1.28

Nock, M. K., & Prinstein, M. J. (2004). A functional approach to the assessment of self-

mutilative behavior. Journal of Consulting and Clinical Psychology, 72, 885-890. doi:

10.1037/0022-006X.72.5.885

Nock, M. K., & Prinstein, M. J. (2005). Contextual features and behavioral functions of self-

mutilation among adolescents. Journal of Abnormal Psychology, 114, 140-146. doi:

10.1037/0021-843X.114.1.140

Nock, M. K., Wedig, M. M., Holmberg, E. B., & Hooley, J. M. (2008). The emotion reactivity

scale: development, evaluation, and relation to self-injurious thoughts and behaviors.

Behavior Therapy, 39, 107-116. doi: 10.1016/j.beth.2007.05.005

Nyhan, W. L. (2005). Lesch-Nyhan disease. Journal of the History of the Neurosciences, 14, 1-

10.

O’Carroll, P. W., Berman, A. L., Maris, R. W., Moscicki, E. K., Tanney, B. L., & Silverman,

M. M. (1996). Beyond the tower of babel: a nomenclature for suicidology. Suicide and

Life-Threatening Behavior, 26, 237-252. doi: 10.1111/j.1943-278X.1996.tb00609.x

Ohmann, S., Schuch, B., Konig, M., Blaas, S., Fliri, C., & Popow, C. (2008). Self- injurious

behavior in adolescent girls. Psychopathology, 41, 226-235. doi: 10.1159/000125556

94

Oldershaw, A., Grima, E., Jollant, F., Richards, C., Simic, M., Taylor, L., & Schmidt, U.

(2009). Decision making and problem solving in adolescents who deliberately self-

harm. Psychological Medicine, 39, 95-104. doi:10.1017/S0033291708003693

Oquendo, M. A., & Mann, J. J. (2000). The biology of impulsivity and suicidality. Psychiatric

Clinics of North America, 23, 11-25.doi:10.1016/S0193-953X(05)70140-4

Osman, A., Hoffman, J., Barrios, F. X., Kopper, B. A., Breitenstein, J. L., & Hahn, S. K.

(2002). Factor structure, reliability, and validity of the Beck Anxiety Inventory in

adolescent psychiatric inpatients. Journal of Clinical Psychology, 58, 443-456.

doi: 10.1002/jclp.1154

Pattison, E. M., & Kahan, J. (1983). The deliberate self-harm syndrome. The American Journal

of Psychiatry, 140, 867-872. Abstract retrieved from

http://ajp.psychiatryonline.org/cgi/content/abstract/140/7/867

Penn, J. V., Esposito, C. L., Schaeffer, L. E., Fritz, G. K., & Spirito, A. (2003). Suicide

attempts and self-mutilative behavior in a juvenile correctional facility. Journal of the

American Academy of Child and Adolescent Psychiatry, 42, 762–769. doi:

10.1097/01.CHI.0000046869.56865.46

Phillips, M. L., Drevets, W. C., Rauch, S. L., & Lane, R. (2003). Neurobiology of emotion

perception I: the neural basis of normal emotion perception. Biological Psychiatry, 54,

504-514. doi: 10.1016/S0006-3223(03)00168-9

Psychological Assessment Resources (1993). Children’s Auditory Verbal Learning Test- 2

(CAVLT-2). Odessa, FL.

Psychological Corporation (1999). Wechsler Abbreviated Scale of Intelligence (WASI) manual.

San Antonio, TX.

95

Richards, J. M., & Gross, J. J. (2000). Emotion regulation and memory: The cognitive costs of

keeping one’s cool. Journal of Personality and Social Psychology, 79, 410-424. doi:

1O.1037/70O22-3514.79.3.410

Robbins, T. W., & Crockett, M. J. (2010). Role of central serotonin in impulsivity and

compulsivity: comparative studies in experimental animals and humans. In C. Muller, &

B. Jacobs (Eds.), Handbook of the behavioral neurobiology of serotonin (pp. 415-427).

Amsterdam: Academic Press. doi: 10.1016/B978-0-12-374634-4.00025-3

Rogers, M. A., Kasai, K., Koji, M., Fukuda, R., Iwanami, A., Nakagome, K., … Kato, N.

(2004). Executive and prefrontal dysfunction in unipolar depression: a review of

neuropsychological and imaging evidence. Neuroscience Research, 50, 1-11.

doi:10.1016/j.neures.2004.05.003

Ross, S., & Heath, N. (2002). A study of the frequency of self-mutilation in a community

sample of adolescents. Journal of Youth and Adolescence, 31, 67-77. doi:

10.1023/A:1014089117419

Ross, S., & Heath, N. L. (2003). Two models of adolescent self-mutilation. Suicide & Life-

Threatening Behavior, 33, 277-287. doi: 10.1521/suli.33.3.277.23218

Ross, S., Heath, N. L., & Toste, J. R. (2009). Non-suicidal self-injury and eating pathology in

high school students. American Journal of Orthopsychiatry, 79, 83-92. doi:

10.1037/a0014826

Rutschmann, J., Cornblatt, B., & Erlenmeyer-Kimling, L. (1977). Sustained attention in

children at risk for schizophrenia. Report on a continuous performance test. Archives of

General Psychiatry, 34, 571-575. doi: 10.1001/archpsyc.1977.01770170081007

96

Salkind, N. J., & Wright, J. C. (1977). The development of reflection-impulsivity and cognitive

efficiency. Human Development, 20, 377-387. doi: 10.1159/000271569

Schmeichel, B. J., Volokhov, R. N., & Demaree, H. A. (2008). Working memory capacity and

the self-regulation of emotional expression and experience. Journal of Personality and

Social Psychology, 95, 1526-1540. doi:10.1037/a0013345

Schmidt, C. A. (2003). Impulsivity. In E. F. Coccaro (Ed.), Aggression psychiatric assessment

and treatment (pp. 75-87). New York: Marcel Dekker, Inc.

Simpson, M. A. (1980). Self-mutilation as indirect self-destructive behavior: “Nothing to get so

cut up about…” In N. L. Farberow (Ed.), The many faces of suicide: indirect self-

destructive behavior (pp. 257-283). New York: McGraw-Hill, Inc.

Skegg, K. (2005). Self-harm. Lancet, 366, 1471-83. doi:10.1016/S0140-6736(05)67600-3

Spielberger, C. D. (1972). Review of profile of mood states. Professional Psychology, 3, 387-

388.

Spielberger, C. D. (1988). State-Trait Anger Expression Inventory. Odessa, FL: Psychological

Assessment Resources.

Stanley, B., Sher, L., Wilson, S., Ekman, R., Huang, Y. Y., & Mann, J. J. (2010). Non-suicidal

self- injurious behavior, endogenous opioids and monoamine neurotransmitters. Journal

of Affective Disorders, 124, 134-140. doi:10.1016/j.jad.2009.10.028

Stanley, B., Winchel, R., Molcho, A., Simeon, D., & Stanley, M. (1992). Suicide and the self-

harm continuum: phenomenological and biochemical evidence. International Review of

Psychiatry, 4, 149-155. doi:10.3109/09540269209066312

97

Steiger, H., Koerner, N., Engelberg, M. J., Israel, M., Ng Ying Kin, N. M. K, & Young, S. N.

(2001). Self-destructiveness and serotonin function in bulimia nervosa. Psychiatry

Research, 103, 15-26. doi:10.1016/S0165-1781(01)00264-5

Strauss, E., Sherman, E. M. S., & Spreen, O. (2006). A compendium of neuropsychological

tests. Oxford: University Press.

Sujansky, R., Griffith, R., & Lefevre, C. (1996). Verbal learning and memory functioning in

learning disabled and non-handicapped lower achieving children: Implications for

diagnosis and educational intervention. Archives of Clinical Neuropsychology, 11, 457-

457(1). doi: 10.1016/0887-6177(96)84023-6

Teri, L. (1982). The use of the Beck Depression Inventory with adolescents. Journal of

Abnormal Child Psychology, 10, 277-284. doi: 10.1007/BF00915946

Talley, J. L. (1993). Children’s Auditory Verbal Learning Test-2 (CAVLT-2). Lutz, FL:

Psychological Assessment Resources.

Van Dillen, L. F., & Koole, S. L. (2007). Clearing the mind: a working memory model of

distraction from negative mood. Emotion, 7, 715-723. doi: 10.1037/1528-3542.7.4.715

Walderhaug, E., Herman, A. I., Magnusson, A., Morgan, M. J., & Landrø, N. I. (2010). The

short (S) allele of the serotonin transporter polymorphism and acute tryptophan

depletion both increases impulsivity in men. Neuroscience Letters, 473, 208-211.

doi:10.1016/j.neulet.2010.02.048

Walderhaug, E., Lunde, H., Nordvik, J., Landrø, N. I., Refsum, H., & Magnusson, A. (2002).

Lowering of serotonin by rapid tryptophan depletion increases impulsiveness in normal

individuals. Psychopharmacology,164, 385-391. doi: 10.1007/s00213-002-1238-4

98

Walderhaug, E., Magnusson, A., Neumeister, A., Lappalainen, J., Lunde, H., Refsum, H., &

Landrø, N. I. (2007). Interactive effects of sex and 5-HTTLPR on mood and impulsivity

during tryptophan depletion in healthy people. Biological Psychiatry, 62, 593-599.

doi:10.1016/j.biopsych.2007.02.012

Walsh, B. W., & Rosen, P. M. (1988). Self-mutilation: theory, research, and treatment. New

York: The Guilford Press.

Weiland-Fiedler, P., Erickson, K., Waldeck, T., Luckenbaugh, D. A., Pike, D., Bonne, O., ...

Neumeister, A. (2004). Evidence for continuing neuropsychological impairments in

depression. Journal of Affective Disorders, 82, 253-258. doi:10.1016/j.jad.2003.10.009

Weltzin, T. E., Fernstrom, J. D., McConaha, C., & Kaye, W. H. (1994). Acute tryptophan

depletion in bulimia: Effects on large neutral amino acids. Biological Psychiatry, 35,

388-397. doi:10.1016/0006-3223(94)90005-1

Whitlock, J., Muehlenkamp, J., & Eckenrode, J. (2008). Variation in nonsuicidal self-injury:

identification and features of latent classes in a college population of emerging adults.

Journal of Clinical Child & Adolescent Psychology, 37, 725-735. doi:

10.1080/15374410802359734

Winstanley, C. A., Dalley, J. W., Theobald, D. E. H., & Robbins, T. W. (2004). Fractionating

impulsivity: contrasting effects of central 5-HT depletion on different measures of

impulsive behavior. Neuropsychopharmacology, 29, 1331-1343.

doi:10.1038/sj.npp.1300434

Young, S. N., Smith, S. E., Pihl, R. O., & Ervin, F. R. (1985). Tryptophan depletion causes a

rapid lowering of mood in normal males. Psychopharmacology, 87, 173-177. doi:

10.1007/BF00431803

99

Zanarini, M. C., Gunderson, J. G., Frankenburg, F. R., & Chauncey, D. L. (1990).

Discriminating borderline personality disorder from other axis II disorders. The

American Journal of Psychiatry, 147, 161-167.

Zepf, F. D., Stadler, C., Demisch, L., Schmitt, M., Landgraf, M., & Poustka, F. (2008).

Serotonergic functioning and trait-impulsivity in attention-deficit/hyperactivity-

disordered boys (ADHD): influence of rapid tryptophan depletion. Human

Psychopharmacology: Clinical & Experimental, 23, 43-51. doi: 10.1002/hup.896

Zepf, F. D., Wöckel, L., Poustka, F., & Holtmann, M. (2009). Dietary tryptophan depletion

according to body weight - a new treatment option in acute mania? Medical Hypotheses,

72, 47-48. doi:10.1016/j.mehy.2008.06.046

Zoroglu, S. S., Tuzun, U., Sar, V., Tutkun, H., Savas, H. A., Ozturk, M., … Kora, M. E. (2003).

Suicide attempt and self-mutilation among Turkish high school students in relation with

abuse, neglect and dissociation. Psychiatry and Clinical Neurosciences, 57, 119-126.

doi: 10.1046/j.1440-1819.2003.01088.x

100

Papers I-III

I

Executive functions are impaired in adolescentsengaging in non-suicidal self-injury

L. T. Fikke1*, A. Melinder1 and N. I. Landrø1,2

1 The Cognitive Developmental Research Unit (EKUP), Department of Psychology, University of Oslo, Norway2 Center for the Study of Human Cognition, Department of Psychology, University of Oslo, Norway

Background. The aim of this study was to investigate three main aspects of executive functions (EFs), i.e. shifting,

updating and inhibition, in adolescents engaging in non-suicidal self-injury (NSSI) as compared with healthy

controls.

Method. EFs were assessed using the Intra/Extradimensional Set Shift, the Spatial Working Memory (SWM) Test

and the Stop Signal Test (SST) from the Cambridge Neuropsychological Test Automated Battery (CANTAB), in a

high-severity NSSI group (n=33), a low-severity NSSI group (n=29) and a healthy control group (n=35). Diagnostic

characteristics were examined using the Kiddie-Sads-Present and Lifetime Version.

Results. There were group differences on the SWM Test. A trend towards an interaction effect of sex revealed that

males in the high-severity NSSI group made significantly more errors than males and females in the control group.

Both males and females in the high-severity NSSI group made poor use of an efficient strategy in completing the test.

The low-severity NSSI group performed poorly on the SST, making more errors than the control group and showing

an impaired ability to inhibit initiated responses, as compared with the high-severity NSSI group. There were group

differences in frequencies of current and previous major depressive disorder. However, no effects of these diagnoses

were found on any of the EF tests.

Conclusions. This study demonstrates that NSSI subgroups have distinct deficits in EFs. The high-severity NSSI

group has working memory deficits, while the low-severity NSSI group has impaired inhibitory control. This

supports the emotion regulation hypothesis.

Received 22 December 2009 ; Revised 6 April 2010 ; Accepted 13 April 2010 ; First published online 19 May 2010

Key words : Adolescence, emotion regulation, executive functions, non-suicidal self-injury.

Introduction

Non-suicidal self-injury (NSSI) is alarmingly wide-

spread in community samples of adolescents (Ross &

Heath, 2002 ; Zoroglu et al. 2003 ; Muehlenkamp &

Gutierrez, 2004, 2007). NSSI involves the deliberate,

direct destruction or alteration of body tissue with

no conscious suicidal intent (Favazza, 1998 ; Lloyd-

Richardson et al. 2007). NSSI is heterogeneous, ranging

from minor to severe forms (Lloyd-Richardson et al.

2007 ; Whitlock et al. 2008) and NSSI behaviours can

be classified into subgroups based on their potential

for causing tissue damage (Skegg, 2005 ; Whitlock

et al. 2008). Some find higher prevalence rates in

girls than in boys (see, for instance, Ross & Heath,

2002), whereas others find no sex difference (see,

for instance, Muehlenkamp & Gutierrez, 2004). Sex

differences in forms and numbers of NSSI behaviours

engaged in exist (Whitlock et al. 2008).

According to the emotion regulation hypothesis,

adolescents engage in NSSI to regulate their emotions,

most often to decrease their negative affective states

(Jacobson & Gould, 2007). This is supported by find-

ings showing that prior to engaging in NSSI, ado-

lescents experience negative emotions, such as anger,

sadness and anxiety, which are reduced during and

especially after having self-injured (Ross & Heath,

2003 ; Laye-Gindhu & Schonert-Reichl, 2005). How-

ever, these findings are exclusively based on ado-

lescents’ retrospective self-reports (Jacobson & Gould,

2007). This confirms the need for exploring the

emotion regulation hypothesis in a more objective

manner.

In a model of the neural basis of emotion proces-

sing, two neural systems underlie neuropsychological

processes that are important for emotional behav-

iour (Phillips et al. 2003). The ventral system, including

the amygdala, insula, ventral striatum, and ventral

* Address for correspondence : L. T. Fikke, Institute of Psychology,

University of Oslo, 0317 Blindern, Oslo, Norway.

(Email : l.t.fikke@psykologi.uio.no)

Psychological Medicine (2011), 41, 601–610. f Cambridge University Press 2010doi:10.1017/S0033291710001030

ORIGINAL ARTICLE

regions of the anterior cingulate gyrus and prefrontal

cortex, is primarily important for the identification of

the emotional significance of a stimulus, the ensuing

production of an affective state, and the automatic

regulation of emotional responses. The dorsal system

includes the hippocampus and dorsal regions of

anterior cingulate gyrus and prefrontal cortex. It is

important for the performance of executive functions

(EFs), which includes effortful regulation of affective

states and emotional behaviours. This involves an

inhibition or modulation of the processes that are

mainly dependent upon the ventral system (Phillips

et al. 2003). Thus, impaired EFs suggest an ineffective

ability to regulate emotions. EFs may be defined as the

skills that are essential for purposeful, goal-directed

activity (Anderson, 1998). Although the different EFs

are interrelated, they are meaningfully diverse abilities

(Miyake et al. 2000). Shifting between mental sets or

tasks, updating and monitoring of information in

working memory (WM), and inhibition of dominant

responses are main aspects of EFs (Miyake et al. 2000).

Although not completely consistent (Herba et al.

2006), some find sex differences in EFs in adolescents

(Anderson et al. 2001 ; Fields et al. 2009).

Only three studies have previously examined

neuropsychological functions in adolescents engaging

in self-injuring behaviours. No differences were found

between adolescents and adults engaging in NSSI as

compared with controls on measures of impulsivity

(Janis & Nock, 2009). Likewise, no differences were

found between adolescents engaging in self-injurious

behaviours and adolescents with none such behav-

iours on tests of EFs (Ohmann et al. 2008). However,

adolescents who currently self-harmed showed im-

paired decision making compared with adolescents

with a previous history of self-injuring, adolescents

with depression and healthy controls (Oldershaw et al.

2009).

The primary aim of the present study was to ex-

plore the main aspects of EFs – shifting, updating and

inhibition – in adolescents engaging in NSSI. Since

adolescents engaging in NSSI constitute a hetero-

geneous group, we examined a high-severity NSSI

group, a low-severity NSSI group in addition to a

control group along these basic dimensions of EFs.

As there may be sex differences in NSSI and EFs, we

investigated the possible interactive effect of sex.

Method

Participants

A total of seventeen high schools in urban and nearby

areas agreed to participate in the study. All grade 9

students present at the schools at the scheduled

times were approached to participate. A total of

327 adolescents were recruited and participated in

the screening session. Group sizes of approximately

30 adolescents would enable us to detect group dif-

ferences (Kyte et al. 2005; Matthews et al. 2008).

To ensure such group sizes in the test session, we

screened until we had 74 adolescents meeting the cri-

teria for inclusion in the NSSI subgroups. The control

group, matched as closely as possible for sex, ethnicity

and school belonging, was randomly selected from

those who had never engaged in any NSSI. This re-

sulted in 116 adolescents being selected to participate

in the test session (74 adolescents in the NSSI sub-

groups and 42 adolescents in the control group). As

13 of these withdrew from further participation, this

left 103 adolescents participating in the test session.

Based on participants’ reported NSSI in the screening

questionnaire and in the section on NSSI in the semi-

structured diagnostic interview in the test session,

participants were classified into three groups : a

high-severity NSSI group (n=33), a low-severity NSSI

group (n=29) and a control group (n=35). Of partici-

pants that had reported that they had never engaged

in NSSI on the screening questionnaire, five revealed

in the interview that they had engaged in one NSSI

behaviour during the past year. They were excluded

from all analyses as they failed to meet the criteria for

any of the groups. Furthermore, due to extreme scores

on several measures, one girl in the control group was

excluded from all analyses.

NSSI was defined as the deliberate, direct destruc-

tion or alteration of body tissue with no conscious

suicidal intent. Acts such as mentally hurting oneself

and engaging in risky behaviours were excluded.

Inclusion in the NSSI subgroups required that the

adolescent had engaged in at least two different NSSI

behaviours during the past year. Participants meeting

these initial criteria were given a score reflecting the

severity of their NSSI. Two NSSI characteristics were

used to calculate the NSSI severity score ; the form(s)

and the total number of different NSSI behaviours

engaged in.

With respect to NSSI forms, NSSI behaviours were

classified into three groups based on their potential for

causing tissue damage (Skegg, 2005 ; Whitlock et al.

2008). Behaviours with potential for superficial tissue

damage were each scored 1, while those with potential

for causing bruising or light tissue damage were each

scored 2. Last, behaviours with potential for causing

severe tissue damage were each scored 3.

To ensure reliability of the classification of NSSI

behaviours into the three groups, training of two

raters was completed, resulting in 90% agreement on

20% of the data. Table 1 summarizes the classification

of NSSI behaviours into the three groups. For each

602 L. T. Fikke et al.

participant meeting the initial criteria for inclusion in

the NSSI subgroups, the weighted scores of the NSSI

behaviours were summarized to give an NSSI severity

score (mean=7.9, S.D.=3.6, median=7.0).

The median was used as the cut-off point separating

the participants into the two NSSI subgroups. Of the

participants, nine scored this value. Of these, five were

classified into the high-severity NSSI group as they

had engaged in NSSI behaviours in all three NSSI

groups, a similar pattern to the majority (i.e. 25 of 28)

of participants in the high-severity NSSI group. The

four remaining participants were classified into the

low-severity NSSI group as they had engaged in NSSI

behaviours in two NSSI groups, either groups 1 and 2

or groups 1 and 3, a similar pattern to the majority

(i.e. 20 of 25) of participants in the low-severity NSSI

group. Table 2 summarizes the number of participants

having engaged in each NSSI behaviour and in each

combination of different NSSI groups, separately for

each NSSI subgroup.

The study was carried out in accordance with

the Helsinki Declaration and accepted by the local

regional ethics committee.

Measures

Symptom assessment

Functional Assessment of Self-Mutilation (FASM). The

FASM (Lloyd et al. 1997, cited by Lloyd-Richardson

et al. 2007) is a self-report questionnaire of the

methods, frequency and functions of NSSI. Studies

with adolescent samples have yielded support for

its psychometric properties (Nock & Prinstein, 2005 ;

Lloyd-Richardson et al. 2007).

Kiddie-Sads – Present and Lifetime Version (K-SADS-PL).

The K-SADS-PL (Kaufman et al. 1997) is a semi-

structured diagnostic interview assessing current and

lifetime history of psychopathology in children and

adolescents according to DSM-IV criteria (APA, 1994).

The following diagnoses were considered particularly

relevant and were examined: major depressive

disorder (MDD), generalized anxiety, obsessive com-

pulsive disorder, panic disorder, social phobia, post-

traumatic stress disorder, anorexia nervosa, bulimia

nervosa, attention deficit hyperactivity disorder,

alcohol abuse and substance abuse.

Beck Depression Inventory (BDI). The BDI (Beck et al.

1988b) is a 21-item self-report measure of depressive

symptoms. Its psychometric properties for use with

adolescents are supported (Larsson & Melin, 1990 ;

Ambrosini et al. 1991).

Beck Anxiety Inventory (BAI). The BAI (Beck et al.

1988a) is a 21-item self-report measure of anxiety. It

shows acceptable psychometric properties in ado-

lescent samples (Jolly et al. 1993 ; Osman et al. 2002).

State-Trait Anger Expression Inventory (STAXI). The

STAXI (Spielberger, 1988) is a self-report measure of

the experience and expression of anger. It has been

used with adolescents (Guertin et al. 2001). Its sub-

scales have adequate internal consistency and con-

struct validity (Spielberger, 1988).

Neuropsychological tests

Wechsler Abbreviated Scale of Intelligence (WASI). The

WASI (Psychological Corporation, 1999) provides a

brief estimate of intelligence. It consists of four sub-

tests : vocabulary, block design, similarities, and

matrix reasoning. The primary variables of interest

were the total intelligence quotient (IQ) score and

the IQ sum scores on the verbal and non-verbal tests,

respectively.

Cambridge Neuropsychological Test Automated Battery

(CANTAB). Tests were selected from the Cambridge

Neuropsychological Test Automated Battery

(CANTAB; Cambridge Cognition, 2006) : obligatory

training tests and EF tests.

Table 1. The categorization of NSSI behaviours into three groups

Superficial tissue damage

(each scores 1)

Bruising and light tissue damage

(each scores 2)

Severe tissue damage

(each scores 3)

Picking at a wound Hitting oneself Cutting or carving one’s skin

Biting oneself Pulling one’s hair out Giving oneself a tattoo

Picking areas of one’s body to the point

of drawing blood

Inserting objects under one’s nails

or skin

Burning

Scraping one’s skin Erasing one’s skin

NSSI, Non-suicidal self-injury.

Executive functions in adolescents engaging in self-injury 603

The obligatory training tests administered were The

Motor Screening test (MOT) and Big/Little Circle

(BLC), which are training tests administered in ad-

vance of other CANTAB tests.

Each of the three EF tests administered measures

each of the main aspects of EFs, i.e. shifting, updating

and inhibition (Miyake et al. 2000).

The Intra/Extradimensional (IED) Set Shift

measures shifting. The subject must learn which of

two presented stimuli is correct, assisted by feed-

back from the computer. Initially, two stimuli of one

dimension (pink shapes) are shown, then each of

two dimensions (pink shapes and white lines) are

shown. The stimuli and/or rules change after six

consecutive correct responses (the criterion of learning

at each stage). These shifts are initially intra-

dimensional (pink shapes are the relevant dimension),

then extra-dimensional (white lines become the rel-

evant dimension). The test terminates if at any stage

the subject fails to reach the criterion of learning after

50 trials. The variables of interest were : stages com-

pleted, pre-ED errors and EDS errors. These reflect the

number of stages completed successfully, the number

of errors made prior to the extra-dimensional shift

and in the extra-dimensional stage of the task, re-

spectively.

The Spatial Working Memory (SWM) test measures

updating and monitoring of spatial information in

WM. The screen displays a number of boxes. The

subject has to find one token in each box and use them

to fill up a column on the side of the screen. Gradually,

the number of boxes increases from three to eight.

Touching any box where a token has already been

found is an error. The subject decides the order in

which boxes are visited. The variables of interest

were total errors and strategy, reflecting the number

of errors made and the use of an efficient strategy for

completing the task, respectively.

Table 2. The number of participants having engaged in each NSSI behaviour and in each combination of different NSSI groups,

separately for each NSSI subgroup

Low-severity

NSSI

(n=29)

High-severity

NSSI

(n=33)

Sum

(n=62)

Superficial tissue damage

Picking at a wound 18 24 42

Biting oneself 13 24 37

Picking areas of one’s body to the point of drawing blood 6 11a 17a

Scraping one’s skin 17 21 38

Other (e.g. scratching oneself, sticking oneself with a needle) 9 14 23

Bruising and light tissue damage

Hitting oneself 10b 19b 29c

Pulling one’s hair out 3 12 15

Inserting objects under one’s nails or skin 1 3 4

Other (e.g. pinching oneself, pulling one’s hair) 5 9 14

Severe tissue damage

Cutting or carving one’s skin 12b 28 40b

Giving oneself a tattoo 0 7 7

Burning 2 8 10

Erasing one’s skin 0 12 12

Other 0 0 0

Combinations of different NSSI groups engaged in

Superficial tissue damage only 3 0 3

Superficial tissue damage+bruising and light tissue damage 13 0 13

Superficial tissue damage+severe tissue damage 11 3 14

Superficial tissue damage+bruising and light

tissue damage+severe tissue damage

2 30 32

NSSI, Non-suicidal self-injury.a Three scores missing.b One score missing.c Two scores missing.

604 L. T. Fikke et al.

The Stop Signal Task (SST; Logan et al. 1984)

measures inhibition of dominant responses. The

screen shows a white ring, in which a left- or right-

pointing arrow is displayed. First, the subject has

to press the left button on a press pad when seeing a

left-pointing arrow, and the right button when seeing

a right-pointing arrow. In the second part of the task,

the subject has to continue pressing the buttons as

before, but has to withhold pressing the button if

hearing a beep. The variables of interest were direction

errors on stop and go trials and stop signal reaction

time (SSRT) last half, expressing the number of times

the subject pressed the wrong button and the ability

to inhibit an initiated response (Eagle et al. 2007),

respectively.

Procedure

A researcher met all potential participants in their

classrooms, informing them about the study. The

adolescents also received written information, includ-

ing information to their parents. Before participation,

all participants and their parents signed an informed

consent. The participants were seen in two sessions.

Screening session

The participants from each school completed the

FASM in a classroom. On the basis of their responses

to the FASM, participants meeting the criteria for

inclusion in the NSSI subgroups were identified.

Test session

All participants met at the Department of Psychology

at the University in Oslo. They completed the follow-

ing tests : MOT, BLC, IED, SWM, SST and WASI.

They also completed BDI, BAI and STAXI. A clinical

psychologist administered the sections covering the

selected psychiatric diagnoses in K-SADS-PL. All

participants were tested individually and were com-

pensated 25 Euros for their participation.

Statistical analysis

SPSS for Windows (version 16.0 ; SPSS Inc., USA) was

used to register and analyse data. To assess group

differences in depressive and anxious symptoms and

anger, one-way between-groups analyses of variance

(ANOVA) were completed. Group comparisons in

frequencies of each diagnosis were performed using

x2 tests.

Scores on the dependent variables on the three EF

tests were converted to Z scores. In doing so, we were

able to make mean Z scores, reflecting the mean scores

of the variables on each EF test for each participant ;

one for the IED test variables, one for the SWM test

variables and one for the SST variables. When positive

scores on the dependent variables on the EF tests

had opposite meanings in their interpretation, some of

them were reversed accordingly.

In instances of group differences in frequencies

of diagnoses, one-way between-groups ANOVA were

conducted to explore the main effects of the particular

diagnoses on the mean Z score of the variables on each

EF test.

To explore main effects of group and sex and

their possible interaction on the mean Z score of the

variables on each EF test, two-way between-groups

ANOVA were performed. Only when these initial

analyses yielded significant effects, further two-

way ANOVA with scores on each variable on the rel-

evant EF test were completed. Post-hoc comparisons

using the least significant difference (LSD) test were

applied. When interaction effects between group and

sex were found, post-hoc comparisons were applied

using a dummy variable with six values represent-

ing the six possible combinations of sex and group

(2r3).

As a criterion of statistical significance, an a level

of p<0.05 was used. Results reaching trend level

(defined as p<0.1) on main or interaction effects are

included and commented on.

Results

Demographic, psychometric and clinical

characteristics

Table 3 summarizes group demographic, psycho-

metric and clinical characteristics. For two girls in

the low-severity NSSI group, current MDD and pre-

vious generalized anxiety, respectively, were scored as

missing as sufficient information was not obtained in

the diagnostic interview. There were no significant

group differences in age, sex ratios or on any IQ

indicators.

There were significant group differences on the

BDI score [F(2, 94)=21.16, p=0.00, g2=0.31] ; the high-

severity NSSI group had a higher score than the

low-severity NSSI group (p=0.00) and the control

group (p=0.00), respectively. The low-severity NSSI

group showed a higher score than the control group

(p=0.00).

The score on the BAI showed significant group

differences [F(2, 94)=11.20, p=0.00, g2=0.19] ; the

high-severity NSSI group had a higher score than both

the control group (p=0.00) and the low-severity NSSI

group (p=0.00).

There were significant group differences on the

STAXI trait score [F(2, 94)=16.70, p=0.00, g2=0.26] ;

Executive functions in adolescents engaging in self-injury 605

the high-severity NSSI group showed a higher score

than both the control (p=0.00) and the low-severity

NSSI group (p=0.00), respectively. Also, the low-

severity NSSI group had a higher score than the con-

trol group (p=0.05). No significant group differences

were found on the STAXI state score.

There were no significant group differences in

frequencies of any diagnoses with the exception of

current MDD (control group=0%, low-severity NSSI

group=10.7%, high-severity NSSI group=21.2%,

x2=8.19, df=2, p<0.02) and previous MDD (control

group=0%, low-severity NSSI group=0%, high-

severity NSSI group=15.2%, x2=10.22, df=2,

p<0.01). However, there was a trend towards signifi-

cant group differences on current social phobia

(control group=0%, low-severity NSSI group=3.4%,

high-severity NSSI group=12.1%, x2=5.35, df=2,

p<0.07).

No main effects of either current or previous MDD

on the mean Z scores of the IED variables, the SWM

variables or the SST variables, respectively, were

found. Accordingly, they were not included in further

analyses.

Performance on EF tasks

Table 4 summarizes performance on all EF tasks, dis-

played by each group and separately for males and

females in each group. Fig. 1 depicts group differences

in scores on the SSRT.

IED variables

No significant group or sex differences or any inter-

action effect between group and sex were found on the

mean Z score of the IED variables.

SWM variables

On the mean Z score of the SWM variables, there

were significant group differences [F(5, 91)=3.98,

p=0.02, g2=0.08]. There were no significant sex dif-

ference or interaction effect between group and sex.

Post-hoc comparisons revealed no significant group

differences.

Significant group differences were found on the

SWM total error score [F(5, 91)=4.08, p=0.02, g2=0.08], but no sex difference was found. There was a

trend towards a significant interaction effect be-

tween group and sex [F(5, 91)=2.75, p=0.07, g2=0.06].

A scatter plot inspection of these results revealed that

the significant main effect of group was caused by

the interaction effect of sex. Post-hoc comparisons

showed that males in the high-severity NSSI group

had a higher score than both males (p=0.00) and

females in the control group (p=0.03).

On the SWM strategy score, there were significant

group differences [F(5, 91)=3.52, p=0.03, g2=0.07] ;

the high-severity NSSI group had a higher score than

the low-severity NSSI group (p=0.04). No significant

sex difference or interaction effect between group and

sex emerged.

Table 3. Demographic, psychometric and clinical characteristics

Healthy

controls

(n=35)

Low-severity

NSSI

(n=29)

High-severity

NSSI

(n=33)

Sex, n (%)

Female 25 (71.4) 22 (75.9) 26 (78.8)

Male 10 (28.6) 7 (24.1) 7 (21.2)

Age, years 14.7 (0.4) 14.7 (0.5) 14.8 (0.4)

Total IQ 100.0 (12.6) 95.6 (11.8) 95.4 (15.3)

Verbal IQ 96.3 (12.7) 93.3 (12.1) 93.8 (14.6)

Non-verbal IQ 104.0 (13.8) 99.0 (12.6) 97.4 (16.4)

BDI 2.6 (3.0) 7.0 (5.2) 11.1 (7.2)

BAI 4.1 (5.0) 6.3 (5.9) 11.3 (8.0)

STAXI

Trait 17.0 (4.0) 20.0 (5.9) 25.3 (7.7)

State 10.3 (1.0) 10.8 (1.8) 11.0 (3.2)

NSSI, Non-suicidal self-injury ; IQ, intelligence quotient ; BDI, Beck Depression

Inventory ; BAI, Beck Anxiety Inventory ; STAXI, State-Trait Anger Expression

Inventory.

Values are given as mean (standard deviation) unless otherwise indicated.

606 L. T. Fikke et al.

SST variables

On the mean Z score of the SST variables, there were

significant group differences [F(5, 91)=6.26, p=0.00,

g2=0.12] ; the low-severity NSSI group had higher

scores than the control group (p=0.02) and the high-

severity NSSI group (p=0.01), respectively.

A trend towards a sex difference [F(5, 91)=3.91,

p=0.05, g2=0.04] was found, while no interaction

effect between group and sex emerged.

On the score on SST direction errors on stop and

go trials, there were significant group differences

[F(5, 91)=4.61, p=0.01, g2=0.09] ; the low-severity

NSSI group had a higher score than the control group

(p=0.03). There were no sex difference or interaction

effect between group and sex.

There were significant group differences on the

score on the SSRT variable [F(5, 91)=6.21, p=0.00,

g2=0.12] ; the low-severity NSSI group had a higher

score than the high-severity NSSI group (p=0.00).

A trend towards a sex difference emerged [F(5, 91)=3.71, p=0.06, g2=0.04], while no interaction effect

between group and sex was found.

Discussion

The main finding in this study was that the high-

severity NSSI group had WM deficits, while the low-

severity NSSI group had impaired inhibitory control.

There were no significant group differences in IQ,

strengthening the conclusion that the results reflect

impairments in specific aspects of EFs and not group

differences in general cognitive abilities. Neither NSSI

subgroups had shifting deficits.

The males in the high-severity NSSI group made

particularly many errors on the WM task, empha-

sizing the importance of examining interaction effects

of sex. Nevertheless, the females in the high-severity

NSSI group also had WM deficits, as shown in their

poor use of the efficient strategy in completing the

task. Males in the low-severity group had the most

impaired inhibitory control ; however, the females in

the same group showed the same pattern.

Our findings replicate previous findings of associ-

ations between NSSI and depressive (Ross & Heath,

Table 4. Summary of results on all executive function tasks in each group and separately for males and females in each group

Healthy controls Low-severity NSSI High-severity NSSI

Total Males Females Total Males Females Total Males Females

IED

Stages

completed

8.4 (0.9) 8.6 (0.8) 8.4 (0.9) 8.3 (0.9) 9.0 (0.0) 8.1 (1.0) 8.6 (0.8) 8.7 (0.5) 8.5 (0.9)

Pre-ED errors 6.5 (1.8) 6.9 (1.4) 6.3 (2.0) 6.8 (2.7) 9.1 (3.3) 6.1 (2.1) 8.1 (3.5) 8.0 (2.0) 8.1 (3.8)

EDS errors 12.7 (10.4) 8.3 (8.9) 14.4 (10.5) 12.5 (12.0) 2.9 (2.3) 15.5 (12.3) 10.0 (9.6) 11.4 (8.5) 9.6 (9.9)

SWM

Strategy 30.0 (4.7) 28.1 (4.5) 30.8 (4.6) 29.3 (5.9) 27.4 (6.3) 30.0 (5.8) 32.1 (5.0) 33.4 (5.7) 31.7 (4.9)

Total errors 14.8 (12.7) 10.0 (11.6) 16.7 (12.8) 19.1 (13.0) 19.0 (10.1) 19.1 (14.0) 20.8 (13.6) 29.0 (8.2) 18.5 (14.1)

SST

Direction

errorsa5.0 (7.1) 4.4 (4.9) 5.2 (7.9) 9.5 (11.3) 15.7 (14.2) 7.6 (9.7) 5.7 (5.7) 7.1 (5.7) 5.3 (5.8)

SSRT 187.7 (48.4) 198.4 (55.9) 183.5 (45.6) 212.0 (60.5) 250.5 (76.7) 199.8 (50.4) 173.3 (39.8) 174.5 (21.4) 173.0 (43.8)

NSSI, Non-suicidal self-injury ; IED, Intra-Extradimensional Set Shift ; Pre-ED errors, errors made prior to the extra-dimensional shift ; EDS

errors, errors made in the extra-dimensional stage ; SWM, Spatial WorkingMemory ; SST, Stop Signal Task ; SSRT, Stop Signal Reaction Time.

Values are given as mean (standard deviation).a Direction errors on stop and go trials.

225

200

175

150

125

SS

RT

Control group Low-severityNSSI group

High-severityNSSI group

Fig. 1. Scores on the Stop Signal Reaction Time (SSRT)

for the three groups. Values are means, with standard

errors represented by vertical bars. NSSI, Non-suicidal

self-injury.

Executive functions in adolescents engaging in self-injury 607

2002; Laye-Gindhu & Schonert-Reichl, 2005) and

anxious symptoms (Ross & Heath, 2002) and anger

control problems (Laye-Gindhu & Schonert-Reichl,

2005). Those meeting criteria for a current or a pre-

vious MDD did not performworse on the EF tests than

those who did not meet the criteria. This indicates that

impairments in EFs in adolescents engaging in NSSI

are not just an expression of an underlying psycho-

logical disorder.

The adolescents in the high-severity NSSI group

had WM deficits, suggesting that their ability to

distract themselves to regulate negative moods is

impaired. By loading WM with tasks demanding

effortful cognitive processing, mood-congruent pro-

cessing can be prevented and thereby result in dis-

traction from negative moods (Van Dillen & Koole,

2007). In this way WM is one mechanism through

which distraction from negative moods operates (Van

Dillen & Koole, 2007) and is thereby related to emotion

regulation.

Following a predetermined search sequence is an

efficient strategy in completing the WM task (Owen

et al. 1990). The poor use of this strategy among ado-

lescents in the high-severity NSSI group suggests that

they struggle in focusing on a specific strategy, reflec-

ting a fundamental deficit in their use of organizational

strategies (Owen et al. 1990). This might complicate

their strategically loading of WM with mood-

incongruent processing, and thereby impair their

ability to distract themselves from negative moods.

Previous findings show a positive association between

strategy score and number of errors (Owen et al. 1990).

For the males in the high-severity NSSI group, the

poor use of the efficient strategy may explain the many

errors they made. However, this does not apply for the

females, making no more errors than the other groups.

This is difficult to explain. Using the efficient strategy

may reduce the loading on WM (Owen et al. 1990).

Apparently females in the high-severity NSSI group

can complete tasks requiring WM, but due to in-

effective organizational strategies, their WM becomes

‘overloaded’. This could impair their ability to distract

themselves from negative moods.

Another mechanism through which emotion regu-

lation occurs is suppression, demanding inhibition

of prepotent responses (Nash et al. 2007). Although

suppression does not provide relief from negative

emotions, it can inhibit emotional behavioural ex-

pression (Gross & Levenson, 1997). In light of the

emotion regulation hypothesis, it is surprising that

the high-severity NSSI group did not have impaired

inhibitory control. In contrast, the impaired inhibitory

control found in the low-severity NSSI group might

suggest an impaired ability to suppress emotional

behavioural expressions of negative emotions.

Our finding of no impaired inhibitory control in

the high-severity NSSI group implies that their self-

injuring is not engaged in impulsively. Although

engaging in similar NSSI behaviours, the high-severity

NSSI group may engage in NSSI behaviours in a more

deliberate, self-injuring way than the low-severity

NSSI group. This is consistent with previous research

showing that adolescents engaging in moderate/

severe NSSI are likely to contemplate NSSI before

engaging in the behaviour (Lloyd-Richardson et al.

2007).

In contrast, the impaired inhibitory control in the

low-severity NSSI group suggests an impulsive

nature of their self-injuring. As there are individual

differences in the degree to which adolescents engage

in emotion-based rash action and risky behaviour

(Cyders & Smith, 2008), the adolescents in the low-

severity NSSI group might be on the one extreme

on this disposition. Accordingly, their self-injuring

might primarily reflect benign, clinically insignificant

experimenting with these behaviours. This is in con-

trast to the self-injuring nature of the same behaviours,

reflecting pathological, clinically significant NSSI

among the adolescents in the high-severity NSSI

group.

With one exception (Oldershaw et al. 2009), our

main findings are inconsistent with previous findings

of no impaired EFs in adolescents engaging in NSSI.

There are several possible explanations for the incon-

sistency. First, previous studies have only had one

NSSI group. As adolescents engaging in NSSI rep-

resent a heterogeneous group (Lloyd-Richardson et al.

2007 ; Whitlock et al. 2008), we classified them into

subgroups, thereby finding distinctive features for

each group. Furthermore, the use of different EF tests

can explain the inconsistency. The theoretically driven

tests used in our study accurately measure each main

aspect of EFs (Robbins et al. 1998 ; Miyake et al. 2000)

and can detect specific impairments in adolescent

populations (Fagerlund et al. 2006 ; Matthews et al.

2008). Last, self-injury has been defined differently

across studies, possibly influencing the findings.

The behaviours that qualify for NSSI and those

that are of clinical significance are unresolved issues

(Lloyd-Richardson et al. 2007). We decided to use as

criteria for inclusion in the NSSI subgroups that the

adolescents had engaged in at least two different NSSI

behaviours during the past year because, first, this

would exclude adolescents only endorsing the item

‘picked at a wound’, as it in isolation may reflect

non-pathological, non-NSSI (Lloyd-Richardson et al.

2007). Second, previous studies (Ross & Heath, 2002 ;

Laye-Gindhu & Schonert-Reichl, 2005) have included

adolescents having only engaged in one NSSI behav-

iour as self-injurers. Thus, our criteria did not seem too

608 L. T. Fikke et al.

liberal. Third, in a community sample of adolescents,

the mean number of different NSSI behaviours per-

formed was 2.35 (Lloyd-Richardson et al. 2007). Our

criteria could not be too conservative relative to this

finding, i.e. it should capture the average adolescent

engaging in NSSI in a community sample.

Furthermore, our procedure for classifying ado-

lescents into the NSSI subgroups was based on a

thorough literature review. The NSSI forms and the

number of different NSSI behaviours engaged in are

particularly important in distinguishing NSSI severity

(Jacobson & Gould, 2007; Whitlock et al. 2008). NSSI

frequency was not included in quantifying NSSI

severity for two reasons. First, its association with

severity is unclear (Jacobson & Gould, 2007). Second,

frequency of NSSI is difficult to assess retrospectively

(Jacobson & Gould, 2007). In accordance with this, a

substantial number of the adolescents in our study

claimed that they did not know or could not remember

how many times they had engaged in NSSI. Thus, we

found NSSI frequency to be a too unreliable criterion

for NSSI severity.

The relatively few males in our sample raises the

question of the reliability of our findings. By inter-

preting our findings as reflecting real group differ-

ences, there is a risk of committing a type I error.

However, rejecting our findings entails the possibility

of committing a type II error. The risks of ignoring our

findings of impairments in EFs in adolescents self-

injuring seem substantial. However, the reliability of

our findings will be strengthened if replicated with

samples including more males. Furthermore, it would

be interesting to explore individual differences within

the NSSI subgroups in future studies.

In addition to impaired EFs, increased emotional

reactivity can constitute a vulnerability for emotional

dysregulation (Nock et al. 2008). Heightened levels of

activity within the ventral system may be associated

with increased emotional reactivity, resulting in ab-

normalities in emotional regulation (Phillips et al.

2003). Including a measure of emotional reactivity in

future research may inform us whether adolescents

engaging in NSSI also have a vulnerability in this

respect.

In conclusion, NSSI subgroups have distinct deficits

in EFs, supporting the emotion regulation hypothesis.

Acknowledgements

We thank all the adolescents who participated in

the study and Ragnhild Bø and Øyvind Bastnes Lie

for their valuable assistance in collecting data. The

study was supported by grants from the Norwegian

Directorate for Children, Youth and Family Affairs

(06/34707) to L.T.F. and A.M.

Declaration of Interest

None.

References

Ambrosini PJ, Metz C, Bianchi MD, Rabinovich H, Undie A

(1991). Concurrent validity and psychometric properties

of the Beck Depression Inventory in outpatient adolescents.

Journal of American Academy of Child and Adolescent

Psychiatry 30, 51–57.

Anderson V (1998). Assessing executive functions

in children : biological, psychological, and developmental

considerations. Neuropsychological Rehabilitation 8, 319–349.

Anderson VA, Anderson P, Northam E, Jacobs R,

Catroppa C (2001). Development of executive

functions through late childhood and adolescence in

an Australian sample. Developmental Neuropsychology

20, 385–406.

APA (1994). Diagnostic and Statistical Manual of Mental

Disorders, 4th edn. American Psychological Association :

Washington, DC.

Beck AT, Epstein N, Brown G, Steer RA (1988a). An

inventory for measuring clinical anxiety : psychometric

properties. Journal of Consulting and Clinical Psychology 56,

893–897.

Beck AT, Steer RA, Garbin MG (1988b). Psychometric

properties of the Beck Depression Inventory :

twenty-five years of evaluation. Clinical Psychology Review

8, 77–100.

Cambridge Cognition (2006). CANTABeclipse Version 3. Test

Administration Guide. Cambridge Cognition Ltd :

Cambridge.

Cyders MA, Smith GT (2008). Emotion-based dispositions to

rash action : positive and negative urgency. Psychological

Bulletin 134, 807–828.

Eagle DM, Baunez C, Hutcheson DM, Lehmann O,

Shah AP, Robbins TW (2007). Stop-signal reaction-time

task performance : role of prefrontal cortex and

subthalamic nucleus. Cerebral Cortex 18, 178–188.

Fagerlund B, Pagsberg AK, Hemmingsen RP (2006).

Cognitive deficits and levels of IQ in adolescent onset

schizophrenia and other psychotic disorders. Schizophrenia

Research 85, 30–39.

Favazza AR (1998). The coming of age of self-mutilation.

Journal of Nervous and Mental Disease 186, 259–268.

Fields S, Collins C, Leraas K, Reynolds B (2009).

Dimensions of impulsive behavior in adolescent

smokers and nonsmokers. Experimental and Clinical

Psychopharmacology 17, 302–311.

Gross JJ, Levenson RW (1997). Hiding feelings : the acute

effects of inhibiting negative and positive emotion. Journal

of Abnormal Psychology 106, 95–103.

Guertin T, Lloyd-Richardson E, Spirito A, Donaldson D,

Boergers J (2001). Self-mutilative behaviour in

adolescents who attempt suicide by overdose. Journal of

American Academy of Child and Adolescent Psychiatry 40,

1062–1069.

Herba CM, Tranah T, Rubia K, Yule W (2006). Conduct

problems in adolescence : three domains of inhibition

Executive functions in adolescents engaging in self-injury 609

and effect of gender. Developmental Neuropsychology 30,

659–695.

Jacobson CM, Gould M (2007). The epidemiology and

phenomenology of non-suicidal self-injurious behavior

among adolescents : a critical review of the literature.

Archives of Suicide Research 11, 129–147.

Janis IB, Nock MK (2009). Are self-injurers impulsive? :

Results from two behavioral laboratory studies. Psychiatry

Research 169, 261–267.

Jolly JB, Aruffo JF, Wherry JN, Livingston R (1993). The

utility of the Beck Anxiety Inventory with inpatient

adolescents. Journal of Anxiety Disorders 7, 95–106.

Kaufman J, Birmaher B, Brent D, Rao U, Flynn C,

Moreci P, Williamson D, Ryan N (1997). Schedule for

affective disorders and schizophrenia for school-age

children – present and lifetime version (K-SADS-PL) :

initial reliability and validity data. Journal of the

American Academy of Child and Adolescent Psychiatry 36,

980–988.

Kyte ZA, Goodyer IM, Sahakian BJ (2005). Selected

executive skills in adolescents with recent first episode

major depression. Journal of Child Psychology and Psychiatry

46, 995–1005.

Larsson B, Melin L (1990). Depressive symptoms in

Swedish adolescents. Journal of Abnormal Child Psychology

18, 91–103.

Laye-Gindhu A, Schonert-Reichl K (2005). Nonsuicidal

self-harm among community adolescents : understanding

the “whats” and “whys” of self-harm. Journal of Youth and

Adolescence 34, 447–457.

Lloyd-Richardson EE, Perrine N, Dierker L, Kelley ML

(2007). Characteristics and functions on non-suicidal

self-injury in a community sample of adolescents.

Psychological Medicine 37, 1183–1192.

Logan GD, Cowan WB, Davis KA (1984). On the ability to

inhibit simple and choice reaction time responses : a model

and a method. Journal of Experimental Psychology : Human

Perception and Performance 10, 276–291.

Matthews K, Coghill D, Rhodes S (2008).

Neuropsychological functioning in depressed adolescent

girls. Journal of Affective Disorders 111, 113–118.

Miyake A, Friedman NP, Emerson MJ, Witzki AH,

Howerter A, Wager TD (2000). The unity and diversity

of executive functions and their contributions to complex

“ frontal lobe” tasks : a latent variable analysis. Cognitive

Psychology 41, 49–100.

Muehlenkamp JJ, Gutierrez PM (2004). An investigation of

differences between self-injurious behavior and suicide

attempts in a sample of adolescents. Suicide and Life-

Threatening Behavior 34, 12–23.

Muehlenkamp JJ, Gutierrez PM (2007). Risk for suicide

attempts among adolescents who engage in non-suicidal

self-injury. Archives of Suicide Research 11, 69–82.

Nash S, Henry JD, McDonald S, Martin I, Brodaty H,

Peek-O’Leary M-A (2007). Cognitive disinhibition and

socioemotional functioning in Alzheimer’s disease.

Journal of the International Neuropsychological Society 13,

1060–1064.

Nock MK, Prinstein MJ (2005). Contextual features

and behavioral functions of self-mutilation

among adolescents. Journal of Abnormal Psychology 114,

140–146.

Nock MK, Wedig MM, Holmberg EB, Hooley JM (2008).

The emotion reactivity scale : development, evaluation,

and relation to self-injurious thoughts and behaviors.

Behavior Therapy 39, 107–116.

Ohmann S, Schuch B, Konig M, Blaas S, Fliri C, Popow C

(2008). Self-injurious behavior in adolescent girls.

Psychopathology 41, 226–235.

Oldershaw A, Grima E, Jollant F, Richards C, Simic M,

Taylor L, Schmidt U (2009). Decision making and problem

solving in adolescents who deliberately self-harm.

Psychological Medicine 39, 95–104.

Osman A, Hoffman J, Barrios FX, Kopper BA,

Breitenstein JL, Hahn SK (2002). Factor structure,

reliability, and validity of the Beck Anxiety Inventory in

adolescent psychiatric inpatients. Journal of Clinical

Psychology 58, 443–456.

Owen AM, Downes JJ, Sahakian BJ, Polkey CE, Robbins

TW (1990). Planning and spatial working memory

following frontal lobe lesions in man. Neuropsychologia 28,

1021–1034.

Phillips ML, Drevets WC, Rauch SL, Lane R (2003).

Neurobiology of emotion perception I : the neural

basis of normal emotion perception. Biological Psychiatry 54,

504–514.

Psychological Corporation (1999). Wechsler Abbreviated Scale

of Intelligence (WASI) Manual. Psychological Corporation :

San Antonio, TX.

Robbins TW, James M, Owen AM, Sahakian BJ,

Lawrence AD, McInnes L, Rabbitt PMA (1998). A study

of performance on tests from the CANTAB battery

sensitive to frontal lobe dysfunction in a large

sample of normal volunteers : implications for

theories of executive functioning and cognitive aging.

Journal of the International Neuropsychological Society 4,

474–490.

Ross S, Heath N (2002). A study of the frequency of

self-mutilation in a community sample of adolescents.

Journal of Youth and Adolescence 31, 67–77.

Ross S, Heath NL (2003). Two models of adolescent

self-mutilation. Suicide and Life-Threatening Behavior 33,

277–287.

Skegg K (2005). Self-harm. Lancet 366, 1471–1483.

Spielberger CD (1988). State-Trait Anger Expression

Inventory. Psychological Assessment Resources :

Odessa, FL.

Van Dillen LF, Koole SL (2007). Clearing the mind :

a working memory model of distraction from negative

mood. Emotion 7, 715–723.

Whitlock J, Muehlenkamp J, Eckenrode J (2008). Variation

in nonsuicidal self-injury : identification and features

of latent classes in a college population of emerging

adults. Journal of Clinical Child and Adolescent Psychology 37,

725–735.

Zoroglu SS, Tuzun U, Sar V, Tutkun H, Savas HA,

Ozturk M, Alyanak B, Kora ME (2003). Suicide attempt

and self-mutilation among Turkish high school students

in relation with abuse, neglect and dissociation. Psychiatry

and Clinical Neurosciences 57, 119–126.

610 L. T. Fikke et al.

II

III